Objective: Need to install an SMTP server (preferably postfix) that will send messages to other common mail providers like gmail, outlook, yahoo, etc.
Problem: Google Cloud blocks usage of SMTP port 25 (but not 465 or 587) and only provides details on how to use external mail providers. Another workaround is to create a gmail account, configure relay as smtp.gmail.com and use the said account to send the messages. The problem with this is that the daily message limit for the relay is probably going to be exceeded with the volume of messages that are expected to be sent.
- Sending a message using mail on ubuntu 18.04 on google cloud using the default postfix configuration and only changing "inet_protocols" to "ipv4". This gives a timeout message on log.
postfix/smtp: connect to ALT2.ASPMX.L.GOOGLE.COM[x.x.x.x]:25: Connection timed out
- Tried changing the following lines in master.cf
smtp inet - - y - - smtpd
smtp unix - - y - - smtp
587 inet - - y - - smtpd
587 unix - - y - - smtp
adding "smtp_use_tls = yes" to main.cf
and restarting postfix. This puts postfix listening and sending messages on port 587, but it still gives the same massage.
postfix/smtp: connect to ALT3.ASPMX.L.GOOGLE.COM[x.x.x.x]:587: Connection timed out
- Messages are sent by using the same configuration as on 1 in another hosting service (port 25 not blocked).
There are people that say smtp between servers only works on port 25, but I've been unable to find any information that confirms this, and not knowing much about mail servers am unsure if it's at all possible to configure another port on postfix for this effect.
Am I just wasting my time trying to configure this on Google Cloud and should just change hosting service? Or is there some kind of way to configure postfix to work with port 25 blocked?