Why did some mailing letters go but not delivered?

Question

linux

Hello. Help, please, to understand.
There was a task to make a mailing list for 15,000 emails. On the Linux server, the Sendmail mail server is installed, the site is on Bitrix. A mailing list was made through the Email marketing module. All 15,000 addresses were sent in 40 - 50 minutes. All addresses were sent without errors, but not all were delivered. Some delivered, some not.
This is what is in the log file:

Aug  1 17:27:11 topligarun sendmail[21745]: v71ERB3k021745: from=<[email protected]>, size=4546, class=-60, nrcpts=1, msgid=<[e-mail]>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]
Aug  1 17:27:11 topligarun sendmail[21744]: v71ERBSB021744: to=[e-mail], delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=142274, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (v71ERB3k021745 Message accepted for delivery)
Aug  1 17:27:12 topligarun sendmail[21747]: STARTTLS=client, relay=gmail-smtp-in.l.google.com., version=TLSv1/SSLv3, verify=FAIL, cipher=ECDHE-RSA-AES128-GCM-SHA256, bits=128/128
Aug  1 17:27:13 topligarun sendmail[21747]: v71ERB3k021745: to=<[e-mail]>, delay=00:00:02, xdelay=00:00:02, mailer=esmtp, pri=232546, relay=gmail-smtp-in.l.google.com. [IPv6:2607:f8b0:4001:c1a::1b], dsn=5.0.0, stat=Service unavailable
Aug  1 17:27:13 topligarun sendmail[21747]: v71ERB3k021745: v71ERD3k021747: DSN: Service unavailable
Aug  1 17:27:13 topligarun sendmail[21747]: v71ERD3k021747: to=root, delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=30000, relay=topligarun.ru. [148.251.182.130], dsn=4.0.0, stat=Deferred: Connection refused by topligarun.ru.
Aug  1 17:28:01 topligarun sendmail[21839]: v71ES1d9021839: from=bitrix, size=692, class=-60, nrcpts=1, msgid=<[e-mail]>, relay=bitrix@localhost
Aug  1 17:28:01 topligarun sendmail[21858]: v71ES1J1021858: from=<[e-mail]>, size=939, class=-60, nrcpts=1, msgid=<[e-mail]>, proto=ESMTP, daemon=MTA, relay=localhost.localdomain [127.0.0.1]
Aug  1 17:28:01 topligarun sendmail[21839]: v71ES1d9021839: to=bitrix, ctladdr=bitrix (600/600), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=138692, relay=[127.0.0.1] [127.0.0.1], dsn=2.0.0, stat=Sent (v71ES1J1021858 Message accepted for delivery)
Aug  1 17:28:01 topligarun sendmail[21860]: v71ES1J1021858: to=<[e-mail]>, ctladdr=<[e-mail]> (600/600), delay=00:00:00, xdelay=00:00:00, mailer=relay, pri=228939, relay=topligarun.ru. [148.251.182.130], dsn=4.0.0, stat=Deferred: Connection refused by topligarun.ru.
Aug  1 17:28:22 topligarun sendmail[21887]: grew WorkList for /var/spool/mqueue to 2000

Answer 1

Reasons are given after stat=

Answer 2

One of the main causes of undeliverable emails is spam traps. They are designed to track spam, if you send an email to them, it will automatically be classified as spam. Since this means that you bought the base or did not assemble it in the right way.
A few more reasons why the mail server may reject the mailing list:
- contacts did not give consent to the mailing list (collected from open sources, purchased, etc.);
- in contacts there is a large% of temporary mails (someone starts them to download a one-time necessary material and not receive mailings, someone for testing), if such addresses are in your database - clean them regularly;
- role addresses in contacts (often they start with info, office, etc.), they rarely subscribe to the mailing list and most likely your letters will at least end up in spam.