I am currently using Evolution for my emails. I set up a VPN a couple of days ago, and now I cannot send emails. If I disconnect the VPN, emails will send. I tried sending through Thunderbird as well with the same issue.
Then there could be the case that your emails hit on the port blocks issued by your VPS provider. You will need to open up a ticket and ask them to remove the email port block so that your emails can go through. If you’re sending via SSL or TSL, then those ports are:
I was using PureVPN and was having this problem all the time on my bank sites and email, I had to shut off the VPN to use them and different programs. I just stopped using it, not worth the trouble.
One thing I discovered today is the following:
Some VPS providers have external firewalls, which block all incoming connections - which would be outgoing for you. IONOS, for example, has that - and we had to open up a port on it just to get through the VPN. Could it be that your own VPS is firewall-ed on the outside?