It's normal that mail server use expired certs?

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I am new to manage a mail server, but since i am a java programmer i 
wanted a software that were easly to adapt to my needs, so when i found 
apache james it fits like a glove.

So in my journey to set it in prod mode i found a lot of problems which 
i could resolve, for example (understad that i was new) SFP, DKIM, 
setting correct ehlo name and similars. But the ones i am no sure if 
have to resolve on my side are those ones involved with TLS 
communication. My servers logs different fails like:

  * unable to find valid certification path to requested target

* Can't verify identity of server: <domain server here>

* Certificate expired

Checking those certs on the target mail server i found that they are to 
old, or self signed, that of course means a configuration problem, but 
they're been running for months even years, if they wouldn't had 
receiving mails they would had correct it, right? so in order for them 
to keep that bad config means other server by passes those native cert 
restrictions and send emails anyway.

So my question is.. do i need to  do that too? this would mean to avoid 
the nature of certs, so if this has to be this way, why concern about 
implementing TLS? just for encryption? I set the remote delivery config 
of verifyServerIdentity to false to bypass one kind of error, but what 
about the others? What do you recommend me to do?


Thanks for your time.

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