LE only provides one type of cert: DV
Which can be used by many devices and service (including email servers).
The best configuration would be one that can be fully automated.
In order to best advise you on how to achieve that, we would have to know some specifics/details.
Like:
- Is the mail server running on the same system as your web server?
[if so, things are simpler; if not, then there are some considerations to deal with and overcome] - Do you have root access to these system(s)?
- [there may be more questions depending on your answers]
That seems to imply that the email server is on the same system - but I take nothing for granted.
Symlinks usually work but that is a general permissions issue.
If they don't work via symlink, it is very simple to include in the process script to copy the files needed to another folder/path where the email system can access them.