Outbound mail routed to recipient spam folders

running MIAB 70 on Ubuntu 20.4 on same server IP# for years. server not listed on any blacklists. too many of my outbound emails are routing into recipient spam folders. what should I check please? are there additional mail integrity actions I should be taking that are not automated via MIAB installation? thank you in advance.

Send yourself a message from MIAB to a gmail account. Inspect the headers by hitting Show Original in the gmail message. See if SPF, DKIM and DMARC are PASS. IF they are FAIL >> Correct the problem. If you wish to see if someone is reporting your messages as Spam in Gmail you must register at their Postmaster tool >> https://postmaster.google.com/v2/ in the New Dashboard there is a User Reported Spam Chart. Also see if you are listed on one of the public blacklists MultiRBL.valli.org - Blacklist, Whitelist and FCrDNS check tool Spamhaus is the most important.