Email Deliverability Guide for B2B Teams

Deliverability is not a single setting. It is the combination of authentication, domain reputation, list quality and recipient behaviour. You can write a good email and still land in spam if the infrastructure is wrong or the list is full of addresses that never asked to hear from you.

1. Authenticate the sending domain

Publish SPF, DKIM and DMARC records for the domain you actually send from. SPF authorises sending servers, DKIM signs the message and DMARC tells receivers what to do when alignment fails. Use a dedicated subdomain for outbound if your main domain also sends transactional mail.

• SPF: keep the record under the DNS lookup limit and remove services you no longer use.
• DKIM: sign with a key you control and rotate it if it may have been exposed.
• DMARC: start with a monitoring policy, review reports, then move to quarantine or reject when the legitimate sources are known.

Authentication does not guarantee inbox placement. It proves the message is allowed to use the domain; reputation and recipient engagement still matter.

2. Warm up slowly

A new domain or IP has no sending history. Start with a small number of recipients who are likely to engage, then increase volume gradually. Keep the daily volume stable rather than jumping from a few messages to thousands overnight. If you change providers, treat the new path as a new warm-up.

Do not use a warm-up tool as a substitute for relevance. Artificial engagement can hide a list-quality problem instead of fixing it.

3. Send to a clean, relevant list

A verified address is not automatically a good prospect. Check that the person still works at the company, that the company matches your market and that the message is relevant to their role. Remove duplicates, role addresses used as personal contacts and anyone who has opted out.

Never cold-mail a purchased or scraped list. High bounce rates and complaints are the fastest way to damage a domain, and the legal risk is unnecessary. Build a smaller list from public business sources and your own research.

4. Handle bounces and complaints

• Hard bounce: remove the address immediately. Do not retry it.
• Soft bounce: retry later, but investigate after repeated failures.
• Complaint: suppress the contact and review why the message missed.
• Unsubscribe: process it within the period required by your jurisdiction and before the next send.

A temporary SMTP response is not a hard bounce. If a verification check is rate-limited or a gateway blocks probes, mark the result unverified and try again later rather than declaring the mailbox dead.

5. Write for a human, not a filter

Plain text, a truthful subject line and one clear call to action are still the safest format for a first touch. Avoid misleading Re: subjects, fake forwards, huge images, shortened links with no context and urgency language. Include your identity and a working opt-out.

Keep the first email short — roughly 80 to 150 words. If the recipient has to scroll to understand why you are writing, the message is too long.

6. Monitor the right signals

Watch bounce rate, complaint rate, unsubscribe rate and replies by campaign. A sudden change in one campaign can point to a bad list segment, a broken link or a copy problem. Check your DMARC reports and your provider's reputation tools, not just the open rate.

Open rates are increasingly unreliable because of privacy features that pre-fetch pixels. Replies, meetings and qualified conversations are better measures of whether the campaign is working.

A pre-send checklist

1. SPF, DKIM and DMARC pass for the sending domain.
2. The domain has a consistent sending history and a gradual warm-up.
3. Every address is verified or honestly marked unverified.
4. Duplicates, role addresses and previous opt-outs are removed.
5. The message includes identity, relevance and a working unsubscribe.
6. Bounce and complaint handling is automated and monitored.

Rasmora's email verifier performs a live SMTP check without sending a message, and labels catch-all or unknown results instead of pretending they are safe. Pair that with the data quality checklist before you import a new segment.