Good morning all,
Apologies to revive this old post, but this is bizarre, and I could not believe it! It just happened last week with Gmail! Never had any issues with deliverability for years now with Gmail.
I use the Linode hosting age of the MIAB, and the mail domain is many years now.
I was e-mailing back and forth with a friend who uses a free Gmail account on 16/01. All was going well, and I was receiving replies, but something happened, and after 18/01, none of my e-mails got to my friend’s inbox ( not even in the SPAM folder ). I tripled checked the MIAB box, and Gmail servers accepted the delivery:
Delivered to a friend’s mailbox:
/var/log/mail.log.2.gz:Jan 10 14:50:10 box postfix/smtp[13400]: 5784D3EC6C: to=<friends_name@gmail.com>, relay=gmail-smtp-in.l.google.com[142.251.5.27]:25, delay=0.81, delays=0.18/0.03/0.33/0.27, dsn=2.0.0, status=sent (250 2.0.0 OK 1641826210 f8si3631088wrw.116 - gsmtp)
/var/log/mail.log.2.gz:Jan 14 16:49:25 box postfix/smtp[16760]: 3F2AF3EA6C: to=<friends_name@gmail.com>, relay=gmail-smtp-in.l.google.com[74.125.206.27]:25, delay=2.1, delays=0.29/0.02/0.39/1.4, dsn=2.0.0, status=sent (250 2.0.0 OK 1642178965 e8si5399428wrj.460 - gsmtp)
/var/log/mail.log.1:Jan 16 09:51:43 box postfix/smtp[31230]: 932173EA5A: to=<friends_name@gmail.com>, relay=gmail-smtp-in.l.google.com[2a00:1450:4010:c09::1a]:25, delay=1.3, delays=0.15/0.02/0.38/0.73, dsn=2.0.0, status=sent (250 2.0.0 OK 1642326703 m9si1517925lfg.254 - gsmtp)
Not reaching my frend’s inbox or SPAM folder, delivered to google servers:
/var/log/mail.log.1:Jan 18 09:35:16 box postfix/smtp[19396]: 8FA6D3E959: to=<friends_name@gmail.com>, relay=gmail-smtp-in.l.google.com[2607:f8b0:400d:c09::1a]:25, delay=2.6, delays=0.36/0.02/0.92/1.3, dsn=2.0.0, status=sent (250 2.0.0 OK 1642498516 di19si5376551qvb.211 - gsmtp)
/var/log/mail.log.1:Jan 20 13:18:48 box postfix/smtp[3109]: 6F43840856: to=<friends_name@gmail.com>, relay=gmail-smtp-in.l.google.com[173.194.79.26]:25, delay=1.7, delays=0.22/0.02/1.3/0.13, dsn=2.0.0, status=sent (250 2.0.0 OK 1642684728 ji18si2352007ejc.687 - gsmtp)
/var/log/mail.log.1:Jan 22 10:29:21 box postfix/smtp[12910]: A72493EACE: to=<friends_name@gmail.com>, relay=gmail-smtp-in.l.google.com[173.194.69.26]:25, delay=1.2, delays=0.12/0.02/0.56/0.53, dsn=2.0.0, status=sent (250 2.0.0 OK 1642847361 lc10si3113007ejc.381 - gsmtp)
Mailing to an old personal Gmail that I do not use for years in Gmail, it was delivered to the SPAM folder:
/var/log/mail.log.1:Jan 20 14:15:33 box postfix/smtp[9199]: CF2E33EECB: to=<my_own_account@gmail.com>, relay=gmail-smtp-in.l.google.com[2a00:1450:4013:c05::1a]:25, delay=1.3, delays=0.17/0.02/0.18/0.88, dsn=2.0.0, status=sent (250 2.0.0 OK 1642688133 4si2260049ejh.192 - gsmtp)
My MIAB IPv4&6 were NOT on any public blocklists. MIAB mostly receive emails, and the monthly emails sent from MIAB is about 30 mails from all mail users in total.
My MIAB personal mail has become very important to me over the last few years, and all my essential government and public services accounts are tight to it and are unaffected by G’s or any other BIG Brothers views on the “small” mail providers 
I have stopped using google and most of its services for a good while now and never coming back, regardless of how they treat my MIAB emails.
My decision to run my mail server will cause a great inconvenience to keep in touch with friends with google mail, but I’ll endure and find alternative channels to communicate with my friends and pay the price to stay as decoupled as I can from the BIGs “free lunch”.
Cheers,