Best Practices for preventing you from looking like a spammer [duplicate]

I can vouch for #2 (reverse PTR) being important, but not #4 (mail server domain matching "from"). We set up mail servers all the time, and most mail hosts don't really even care about #2.

The main thorn is always AOL, and they list standards you can check off.

Aside from your HELO string and the DNS PTR records as mentioned, the bulk of the things that will help are going to be content related, not sending-sever related.

• Don't send out HTML email if you can at all avoid it.
• Don't include suspect phrases ("click to unsubscribe","privacy is important" and the like)
• Don't use "reply-to" headers, send from the address you wish responses to go to
• ...and more. Read the SpamAssassin ruleset for more good examples.

As to your question of "does it care what that FQDN resolves to?", this is entirely dependent on what the receiving mail server does, and it of course can vary, but you typically won't find too many mail servers relying on the FQDN lookup as a hard and fast rule, since it's possible to have multiple machines configured in a round-robin setup.