If a displayname equals to the address, adding it looks excessive.
Moreover, it's not useful for Delta Chat receiving the message because
`sanitize_name_and_addr()` removes such a displayname anyway. Also now
at least DC Android requires specifying profile name, so there should be
a fallback for users having meaningful addresses to keep the old
behaviour when Core generates `From` w/o the profile name, and this
question has already appeared on the forum.
I.e. treat `DeleteServerAfter == None` as "delete at once". But when a backup is exported, set
`DeleteServerAfter` to 0 so that the server decides when to delete messages, in order not to break
the multi-device case. Even if a backup is not aimed for deploying more devices, `DeleteServerAfter`
must be set to 0, otherwise the backup is half-useful because after a restoration the user wouldn't
see new messages deleted by the device after the backup was done. But if the user explicitly set
`DeleteServerAfter`, don't change it when exporting a backup. Anyway even for non-chatmail case the
app should warn the user before a backup export if they have `DeleteServerAfter` enabled.
Also do the same after a backup import. While this isn't reliable as we can crash in between, this
is a problem only for old backups, new backups already have `DeleteServerAfter` set if necessary.
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Co-authored-by: Hocuri <hocuri@gmx.de>
iequidoo
