Incoming email problem

Dear Virtualmin Forum members,

My webmin/virtualmin sending emails without any problem but problem in incoming emails, emails not coming, whats the reason and how can I set its.

and sometimes emails received after 10 to 12 hours. why?

Thanks & Regards

Hi did you actually read the docs from virtualmin?

can u refer me the docs.

gmail show this error:

The response was:
read error: FAILED_PRECONDITION: read error (104): Connection reset by peer.

and yahoo shown:

Sorry, we were unable to deliver your message to the following address.
Unable to deliver message after multiple retries, giving up.

Help me in this regard please.