When I first created the mail server everything worked fine and mail landed in the inboxes of Gmail accounts.

Now all of the sudden it keeps landing in Spam boxes. I even added SPF records and an Let's Encrypt SSL certificate. I found myself blacklisted while only 30 mails have been send as test to myself. I was blacklisted by ivmSIP/24. After requesting removal yesterday, this morning I confirmed they removed me from their blacklist.

What is going and how do I trouble shoot beyond the things I have done?

My mail server scores better then my work mail server which doesn't land in the spambox.

Results from http://isnotspam.com

• 3.5 BAYES_99 BODY: Bayes spam probability is 99 to 100%
• [score: 1.0000]
• -0.0 SPF_PASS SPF: sender matches SPF record
• -0.0 RPMATCHESRCVD Envelope sender domain matches handover relay domain
• 0.2 BAYES_999 BODY: Bayes spam probability is 99.9 to 100%
• [score: 1.0000]
• 0.1 HTML_MESSAGE BODY: HTML included in message
• 0.1 DKIM_SIGNED Message has a DKIM or DK signature, not necessarily
• valid
• 0.0 TDKIMINVALID DKIM-Signature header exists but is not valid X-Spam-Status: Yes, hits=3.9 required=-20.0 tests=BAYES99,BAYES999, DKIMSIGNED,HTMLMESSAGE,RPMATCHESRCVD,SPFPASS,TDKIMINVALID autolearn=no autolearnforce=no version=3.4.0 X-Spam-Score: 3.9

Results from MXtoolbox mail server test:

SMTP Reverse DNS Mismatch OK - 1.2.3.4 resolves to mail.myserver.io
SMTP Valid Hostname OK - Reverse DNS is a valid Hostname
SMTP Banner Check OK - Reverse DNS matches SMTP Banner
SMTP TLS OK - Supports TLS.
SMTP Connection Time 1.125 seconds - Good on Connection time
SMTP Open Relay OK - Not an open relay.
SMTP Transaction Time 3.641 seconds - Good on Transaction Time