On the server, MX records are configured to send mail to the mailbox created in webmail, the name of the mailbox looks like example@finestra.biz
If you send letters to this mailbox from simple mailboxes, then there is no problem, but if the server on which the site is located, then nothing happens, for example, just through mail (example@finestra.biz, "test", "test") the problem is wrong setting MX records?
Or something else could be? Before that, they say the mail seemed to work and I still know that this mailbox is set up with some kind of mail client, but this cannot but influence the work of the mailbox? Most likely that on the server we have not properly configured?