I am unable to send emails to gmail. I am sending the emails through Usermin, by making an email account on Virtualmin. I am able to send and receive emails between virtual servers made on Virtualmin, but whenever I try to send the email my gmail account, it get’s queued up in the Postfix Mail Queue. I am fairly new to mail servers, so any help will be appreciated.
You’ve got the answer right there then.
Most residential ISPs block port 25 (like a lot of cloud providers also starting to do by default) to prevent abuse.
Contact them to see if there’s any chance of lifting the block or send through a relay.
Follow advice from @toreskev, if ISP can’t unblock as most block port 25. You may be able to use 465 and 587. Would have been nice to see the above in original query as it would have explained everything as to why you have this problem.
Just know that you won’t be able to send mails to other MTAs using different ports than 25, as this is the default MTA <-> MTA communication port.
If you’re interested, you are welcome to try out my mail relay service which I’m planning/hoping to launch shortly™, free of charge of course.
Just drop me a PM if you want.