How do you send a sales email without landing in spam?

For a sales email to work, it first has to be read, and to be read, it first has to stay out of the spam folder. Two things decide this: whether the address you send from is technically authenticated, and how recipients react to your email. The rules below come from Gmail's and Yahoo's own documentation.

1. Authenticate your address: SPF, DKIM, DMARC

These three acronyms are records that prove an email really comes from your domain.

SPF: lists which servers are allowed to send email on behalf of your domain.
DKIM: adds a digital signature to the email showing it has not been altered.
DMARC: ties SPF and DKIM together and tells the receiving server what to do if authentication fails (monitor, quarantine, reject). The DMARC standard is defined in RFC 7489.

Gmail requires SPF or DKIM from all senders, and all three from those sending more than 5,000 messages a day. Since February 2024, Yahoo has also expected SPF or DKIM from all senders, both from bulk senders, and a DMARC policy of at least "p=none". Even if your sending volume is small, setting up all three is a sound and inexpensive safeguard.

2. Keep your complaint rate low

Gmail and Yahoo look at the spam complaint rate:

Gmail recommends keeping the spam rate in Postmaster Tools below 0.10% and never letting it reach 0.30%.
Yahoo asks for the spam rate to stay below 0.3%.

In short, a rate of 0.3% means 3 out of 1,000 recipients complaining. Staying below that is essential; below Gmail's target of 0.1% means fewer than 1 in 1,000. That is why the goal is not to reach many people but to reach the right people.

3. Add one-click unsubscribe

Gmail asks that marketing emails support one-click unsubscribe, and Yahoo asks the same of bulk senders. This is done with the "List-Unsubscribe-Post" header from RFC 8058. Yahoo recommends honouring unsubscribe requests within 2 days, and Gmail within 48 hours. The unsubscribe link can sit small and simple at the very bottom of the email, below the signature; what matters is that it works.

4. Write one by one, not in bulk

Gmail defines a "bulk sender" as anyone sending roughly 5,000 or more messages to personal Gmail addresses. A small business stays well below that threshold, but the rule works on the same logic: sending the same text to hundreds of people brings complaints, while a short email written specifically for a relevant person does not. In practice:

Include a sentence in every email that is specific to the recipient's business.
Make one question or one suggestion.
Do not use a misleading subject line; it should say what the email contains.
Spread your sending across the day rather than sending many in the same minute.
Do not write again straight away to someone who has not replied. Wait a long time after the first email, and then send only a single, short reminder.

Note: we could not find a primary source showing the effect of personalisation on delivery or reply rates, so we do not give a figure.

5. Monitor after sending

Check your spam rate in Postmaster Tools.
Remove bounced (undelivered) addresses from your list.
Do not write again to anyone who asks you not to.

Because these tasks repeat, they suit automation well. At aideago, the sales representative agent writes every proposal specifically for a single business, records unsubscribe requests and bounces, and updates the list accordingly.