Email: Adds note about regen-conf use

[mediaformat]

Adds note about regen-conf use

Problem

• Looking through the Email section of the documentation did not help me find any clues to fix my config. (broken since Yunohost 12.1 release)

Solution

• Adding this note for awareness of the command, in the most relevant public doc place I would look.

PR checklist

• PR finished and ready to be reviewed

[Salamandar]

I don't really get it. You usually never have to edit manually the config. When are you expected to run regen-conf ?

[mediaformat]

I don't really get it. You usually never have to edit manually the config. When are you expected to run regen-conf ?

@Salamandar In my experience, having reject_rbl_client cbl.abuseat.org, meant anything from Gmail was blocked.
That was the only, but very compelling reason to modify it.