test email port: telnet portquiz.net anyport
telnet alt3.gmail-smtp-in.l.google.com 25
Mailwizz server: https://scribeage.com/services/
《setup mailwizz server》
PowerMTA https://technicalsahil.com/how-to-install-setup-powermta-smtp-server-on-centos-7/
https://www.temporary-mail.net/
Docker mail server: https://mailu.io/
email title check： https://sendcheckit.com/
how to know email ip address clear? https://check.spamhaus.org/
Google email toos: https://toolbox.googleapps.com/apps/main/
Google email head check tools: https://toolbox.googleapps.com/apps/messageheader/
email record check tools: https://mxtoolbox.com/
send email ok test tool: https://www.lemwarm.com/deliverability-test
DKIM check: https://dmarcian.com/dkim-validator/
About DKIM(by japanese) https://baremail.jp/blog/2023/10/13/3528/
black list check https://multirbl.valli.org/lookup/
Google email bot ip: https://github.com/pksh71/gmail-bot-email-open-click-ip-ranges