Automated emails: what headers are important to ensure delivery?

[csdude55]

I'm trying to go through every step possible to make sure my user-requested email is delivered.

It turns out that there are a bajillion potential mail headers:

[cs.tut.fi...]

So far, I'm setting To, From, Date, Message-ID, and Subject, but still being filtered as spam by Gmail (even though I have a +0.1 SpamAssassin score, a 100 SenderScore, and Mail-Tester.com gives me a 10/10... grrr).

What other headers might I want to consider adding to make sure I'm not getting filtered?

[keyplyr]

Don't know much more than you do about mail headers.

At my mail server, I set my own filters entirely by Sender, Recipient and terms found in Subject as well as the content (buzz words.) I have a similar system at my email client.

[phranque]

have you looked at implementing the SPF protocol?

Sender Policy Framework (SPF) for Authorizing Use of Domains in E-Mail, Version 1:
https://www.rfc-editor.org/rfc/rfc4408.txt [rfc-editor.org]

SPF: Project Overview:
http://www.openspf.org/ [openspf.org]

[Jonesy]

Yes. SPF and DKIM

Any "secret" headers that you seek to allow your emails to slip past spam filtering
would've been implemented by the sime-ball spammers YEARS AGO.