Hey there! I'm sorry to hear about these mail issues on the system. If you aren't able to send or
receive, the most likely explanation is that your hosting provider is blocking port 25 on your server. The support article linked below has a list of providers that are known to block the email ports on their network, plus some troubleshooting tips so you can see if that is the case:
Symptoms When trying to send mail from your server, the mail is never sent. Connections to other servers on port 25 refuse to connect. Description Many providers block access to send data out on...
Can you work through that and see if that is indeed the issue?