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Optimising Email-Sending Infrastructure: How to Ensure Delivery in B2B Outbound

In this guide, you'll get a practical roadmap on how to set up your technical infrastructure for outbound email.

Mario Sinz

Chief Growth at Leadtree

Published on

If your outbound emails land in spam, the best pitch won't help you. For B2B tech startups and scale-ups, a clean email sending infrastructure is just as important as good targeting today – otherwise, the sales funnel breaks down before the first open.

In this guide, you'll get a practical roadmap on how to set up your technical infrastructure for outbound email.

  • clean shipping domains and sender structure
  • Correctly configure SPF, DKIM, and DMARC
  • Plan IP and domain warmup
  • Keep an eye on reputation, lead tracking and KPIs

This makes your outbound channel more predictable – and minimises the risk of damaging your main domain.

What you need for a stable outbound email infrastructure

Before you start optimising, a few technical and organisational basics should be clarified:

  • Primary company domain e.g. startupname.com or .io.
  • Custom outbound sending domains – ideally „cousin domains“ or subdomains close to the brandhello-startupname.com, outbound.startupname.comThis protects your main domain's reputation during cold campaigns.suped.com)
  • Access to DNS management – to set SPF, DKIM and DMARC TXT records.
  • Email provider or outreach tool – e.g. a dedicated SMTP provider or a cold email/outbound tool with tracking, bounce handling and simple limits.
  • Monitoring Accounts – e.g. Google Postmaster Tools and Microsoft SNDS, to track reputation and delivery rates.chillmail.io)
  • Clearly defined KPIs for outbound – Bounce rate, spam complaint rate, qualified appointments, and pipeline value. At Leadtree, such metrics are standardised via dashboards and KPI reporting to make ROI transparent.
  • Legal certainty – Clarify GDPR/UWG compliant procedures with your legal department before scaling.

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Step-by-step guide: Technical basis for high delivery rates

Step 1: Set up sending domains and sender structure cleanly

What you should do

  1. Separate critical email types:
    • Main domain for:
      • Transactional emails (login, password reset, invoices)
      • Manual 1:1 communication from the inbox
    • Subdomain or separate, brand-related domain for:
      • Outbound / cold emails
      • Newsletter & Marketing Automation
  2. Choose close-fitting domains:
    • Guts startupname.io -> hello-startupname.com or try-startupname.com
    • Poor: generic, unassignable domainsb2b-sales-mailz.netThis comes across as unprofessional and triggers filters.suped.com)
  3. Structure sender addresses:
    • Is the Outbound Inbox clear address: vorname@hello-startupname.com
    • No function addresses like sales@ or info@ for cold campaigns – automatically appear like mass mailings.

Why this is important

  • Cold outbound campaigns naturally have higher bounce and spam risks.
  • If you send everything about the main domain, you risk product emails and important sales communications also ending up in the spam folder.suped.com)
  • Through separation, you can cleanly track reputation, volume, and KPIs per stream.

Typical mistakes

  • Cold mass outreach from @startupname.com without separate infrastructure.
  • Anonymous senderssales@...), which immediately arouse suspicion in B2B inboxes.
  • Too many different domains, which according to Spamhaus and deliverability experts can again be regarded as a spam signal.suped.com)

Step 2: Correctly configure SPF, DKIM and DMARC

In brief:

  • SPF (Sender Policy Framework)Specifies which servers/IP addresses are permitted to send emails for your domain in a DNS record. This allows recipients to check if the source is legitimate and block direct spoofing attempts.en.wikipedia.org)
  • DKIM (DomainKeys Identified Mail)Signs each email cryptographically with a private key; the public key is in the DNS. Recipients can thus see that the message has not been tampered with in transit and is indeed signed by your domain.biscred.com)
  • DMARC (Domain-based Message Authentication, Reporting and Conformance): Links SPF and DKIM results to the visible sender address and defines what should happen when authentication fails (allow, move to spam, or reject). DMARC also provides reports on successes and failures.techtarget.com)

Concrete implementation steps

  1. Setting up SPF:
    • Create DNS TXT records for each sending domain, e.g.:
      • v=spf1 include:_spf.provider.com ~all
    • Take care, only one SPF record per domain to have; several records lead to errors.
  2. Activate DKIM:
    • Generate DKIM key in the email/outreach tool.
    • Public key as a TXT record (usually selector._domainkey.deinedomain.comto add to the DNS.
    • Send a test email to a deliverability testing tool and check if „DKIM=pass“ is displayed.
  3. Building DMARC step-by-step:
    • Start with Monitoring Policy:
      • v=DMARC1; p=none; rua=mailto:dmarc-reports@deinedomain.com; fo=1
        Emails won't be blocked, but you will receive reports.
    • After 2-4 weeks of stable authentication, gradually increase the strength:
      • p=quarantine (suspicious emails in spam)
      • later p=reject (Incorrect emails will be rejected).techtarget.com)

Typical mistakes

  • SPF record too many include:-entries or more than ten DNS lookups – some providers consider this to be faulty.
  • DMARC directly on p=reject to set without checking reports and alignment beforehand.
  • Different from-domains in tools that do not match the authenticated domains – DMARC alignment then fails.

Step 3: Systematically plan IP and domain warm-up

What is IP/domain warmup?

IP-Warmup means increasing the sending volume over a new IP address or sending domain to increase step-by-step, so that providers can build trust and your sender reputation is not classified as spam.poptin.comIn practice, this process typically takes 2-4 weeks or longer.(support.optimizely.com)

Outbound Practice Plan (per Inbox)

  • Week 1:
    • 20-30 e-mails/day to the warmest contacts (existing leads, partners, opt-in contacts).
  • Week 2:
    • 40-60 emails/day.
  • Week 3:
    • 70-100 emails/day, first cold ICP accounts with high fit.
  • Week 4+
    • Gradually increase to 120-150 emails/day per inbox – only if KPIs are stable.

Key target values during warm-up

  • Bounce Rate Permanent < 2 % Striving for > 5 % is a clear warning sign of data or infrastructure problems.(suped.com)
  • Spam complaints: as much as possible Below 0.1 % the recipient.artemisleads.com)
  • Open Rate: ideally 20 % – particularly in the first few weeks.

Typical mistakes

  • Start directly with several thousand cold emails per day.
  • Multi-day broadcast pauses in warmup – providers like Consistent patterns and regular volumes.support.optimizely.com)
  • Mixing warm and completely cold lists without segmentation.

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Step 4: Set up Monitoring, Lead Tracking & KPI Reporting

A clean infrastructure without reporting is like a CRM without deals. For professional B2B sales, you need clear metrics across the entire outbound process.

Technical KPIs for Deliverability & Reputation

  • Delivery rate Delivered vs. Sent
  • Bounce rate (Hard vs. Soft Bounces Separated)
  • Spam complaint rate
  • Inbox Placement Inbox vs. Promotions vs. Spam – about Seed Tests/Tools

Sales KPIs for your funnel

  • Open Rate / Reply Rate per sequence and ICP cluster
  • Positive Replies (Interest, Deadline) vs. Negative Replies (Opt-out, „no need“)
  • End of contract 100 emails sent
  • Pipeline Value & Revenue per Campaign

Leadtree works on social selling and outbound projects with standardised dashboards to make key figures such as conversion rate, cost per lead, and pipeline value transparent at all times – this is precisely the standard that should also apply to your e-mail channel.

Tools & Processes

  • Provider-specific tools (Google Postmaster, Microsoft SNDS) for reputation and spam rates.chillmail.io)
  • CRM integration (HubSpot, Pipedrive, Salesforce) to track from email event -> lead -> opportunity -> revenue.
  • Weekly review calls within the team (or with the agency) to discuss KPIs and optimise sequences.

Typical mistakes

  • Only look at open rates, but ignore bounce and complaint rates.
  • No clear separation of technical deliverability KPIs and sales success metrics.

Step 5: Integrate list hygiene & shipping logic into your outbound automation

Even though this guide focuses on technology: Sound quality and shipping logic are central to your reputation.

Best Practices

  1. Regular list cleaning:
    • Immediately remove hard bounces permanently.
    • Consistently pause inactive contacts (x campaigns with no opens/replies).
  2. Engagement segmentation
    • Warm-up phase: highly engaged contacts only.
    • Afterwards, gradually expand to less active or new ICP lists – always with an eye on the overall KPIs.chillmail.io)
  3. Rules in your outbound automation:
    • Immediate stop of further steps after hard bounce or spam complaint.
    • Automatic logout/tagging for „Please no more emails“.
  4. Limit per Inbox & Tag:
    • For cold emails, it’s better to run multiple inboxes with moderate volume than a few accounts at their limit. Recommendations from deliverability guides are often at 25-30 cold emails per inbox/day after Warmup – scale via additional Inboxes as needed.instantly.ai)

Typical mistakes

  • Purchased lists without validation.
  • No clear opt-out, which unnecessarily increases complaints.
  • Too aggressive automation without human control.

Do you want to understand how we connect social selling on LinkedIn with email outbound?

Arrange a free strategy meeting. 

Pro-Tips & Best Practices für anspruchsvolle Setups

  1. Making effective use of DMARC reports
    Use the aggregate reports to see how providers are judging your emails, whether there are unknown sending sources, and how your policy tightening (none -> quarantine -> reject) is affecting things.techtarget.com)
  2. Multiple inboxes instead of one „super inbox“
    Scale cold outbound volumes across multiple cleanly warmed mailboxes and domains. This distributes risk and keeps each account within a „natural“ volume range.instantly.ai)
  3. Multi-channel instead of e-mail only
    Studies and practical data show that coordinated sequences across LinkedIn, E-mail, Telephone achieve significantly higher response rates on average than single-channel campaigns. Particularly in the B2B tech environment, social selling on LinkedIn works particularly well in conjunction with good outbound email.
  4. Review Done-for-You for complex infrastructures
    The more domains, tools, and countries involved, the more susceptible the setup becomes to errors. Leadtree uses more than 18 tools for targeting, automation, and personalisation in client projects, coupling them with transparent KPI reporting – a setup that many in-house teams don't want to build due to time and resource constraints.
  5. Bringing Sales and Tech Together Early
    Deliverability is not purely an IT issue. Ensure that sales, marketing, and IT jointly define which KPIs are important, which lists are considered „clean,“ and how new campaigns are launched from a technical perspective.

Troubleshooting: Common Problems & Quick Solutions

Problem 1: Your emails are suddenly ending up in spam

Possible causes

  • DMARC/SPF/DKIM incorrectly configured or recently changed
  • Sudden volume jump (e.g., 10x more sends than usual)
  • Poor list quality, high bounce and complaint rates
  • Content with typical spam signals (attachments, „hard“ phrasing, many links)

Solution (Short Checklist)

  1. Check authentication: Validate SPF record, perform DKIM test, check DMARC status.
  2. Turn down the volume Reduce sending volume for 1-2 weeks and resume warm-up process.
  3. Clean list: Remove hard bounces and inactive contacts.
  4. Defuse content Fewer links, a clearer focus on plaintext, personalised subject lines.

Problem 2: Bounce-Rate > 5 % after campaign launch

Possible causes

  • Outdated or unvalidated email lists
  • Technical problems with the provider (incorrect HELO, blocked IPs)
  • Sending to domains with strict policies without warmup

Solution

  1. Stop immediately Pause campaign to protect reputation.
  2. Validate list: Use e-mail verification tool, sort out hard bounces.
  3. Plan restart: Restart with significantly reduced volume and better lists; bring bounce rate back under 2-3 %.suped.com)

Problem 3: Open rates plummet after domain or tool change

Possible causes

  • New domain/IP without sufficient warmup
  • SPF/DKIM not correctly set up on new infrastructure
  • „Carried over“ negative reputation from previous campaigns“

Solution

  1. Re-perform IP/domain warmup – with a focus on highly engaged segments.poptin.com)
  2. Check DNS records Do SPF, DKIM, and DMARC apply to the new domain?
  3. Implement Seed-Tests Create inboxes with different providers to measure inbox placement.

Do you want to understand how we connect social selling on LinkedIn with email outbound?

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Frequently Asked Questions (FAQ)

Do I need a dedicated IP address for outbound emails as a B2B startup?

Not necessarily. Many providers use shared IP pools with good reputations, which are perfectly adequate for moderate volumes. A dedicated IP is worthwhile if you send very high volumes or need maximum control over your reputation – in that case, IP warmup is mandatory, and you bear full responsibility for bounce and spam rates.support.optimizely.com)

2. How many cold emails can I safely send per day?

This depends on domain age, reputation, and list quality. Best practice in the cold email environment:

  • After warm-up 25-30 cold emails per inbox per day
  • Scaling using additional, cleanly warmed inboxes and domains, rather than pushing individual accounts to their limits.instantly.ai)

More important than a fixed number are stable KPIs: bounce rate < 2 %, spam complaints significantly < 0.1 %.

3. How long does it take for my deliverability to stabilise?

Plan at least 2-4 weeks to, in order to seriously warm up a new shipping domain and IP.support.optimizely.comDuring this time, you should closely monitor volume and engagement and only increase them cautiously.

4. Can I adopt my LinkedIn outreach strategy 1:1 for email?

In terms of content, you can reuse many elements (ICP clusters, trigger events, psychologically optimised messaging) – Leadtree works cross-channel in exactly the same way. Technically, however, email is more sensitive: domain, IP, and reputation issues play a much larger role than with LinkedIn DMs. Therefore, you should test copy & sequences per channel and evaluate KPIs separately.

5. From when is a done-for-you setup for email infrastructure worthwhile?

At the latest, when you:

  • you want to serve several markets/target groups in parallel,
  • intern keinen dedizierten Verantwortlichen für die Zustellbarkeit hast,
  • or already had initial reputational problems (spam, blocklists).

Then, a specialised partner who handles the tech stack, sequences, KPI reporting, and appointment setting is often more cost-effective than internal learning curves. Leadtree operates exactly like this in social selling: monthly cancellation, no setup fee, and with an appointment/performance guarantee – this model can also be applied to more complex outbound setups, including email.

What is the next sensible step?

Once your email-sending infrastructure is properly set up, you should next:

  • yours ICP cluster and trigger events sharpen (Funding, Hiring, Tool Change, Expansion),
  • Messaging-Playbooks develop which specifically in terms of outcomes and ROI deposit,
  • Email sequences with LinkedIn Outreach and Social Selling interlock to reach your target accounts across multiple touchpoints,
  • and a repeatable Reporting Setup building, that measures end-to-end from email KPIs to booked appointment and revenue.

If you lack internal resources, tool know-how, or time for this, a done-for-you setup with a clear deadline and performance guarantee can make all the difference – freeing you up to focus on product, team, and funding once again.

Key Takeaways

  • Separate your shipping domainsProtect main domain, run outbound traffic via brand-related domains/subdomains.
  • SPF, DKIM and DMARC are mandatoryWithout clean authentication, reliable deliverability in B2B is hardly possible.
  • Warm-up is not a nice-to-haveNew domains and IPs require 2-4 weeks of controlled volume build-up.
  • Reputation is data-drivenBounce, complaint, and engagement KPIs are an integral part of your sales reporting.
  • Complexity calls for professional supportAt a certain scale, a Done-for-You setup that integrates technology, automation, and appointment booking becomes worthwhile.

Do you want to understand how we connect social selling on LinkedIn with email outbound?

Arrange a free strategy meeting. 
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