`strftime`'s formatting is locale-dependent. If the system locale was
set to e.g. de_DE.UTF-8, the `Date` header became invalid
(e.g Mo instead of Mon for 'Monday'), tripping up some mail clients
(e.g. KMail).
This commit should fix this by using the new `epoch_to_rfc2822`
function from proxmox_time. Under the hood, this function uses
`strftime_l` with a fixed locale (C).
Signed-off-by: Lukas Wagner <l.wagner@proxmox.com>
`Auto-Submitted` is defined in the rfc 5436 [1] and describes how
an automatic response (f.e. ooo replies, etc.) should behave on the
emails. When using `Auto-Submitted: auto-generated` (or any value
other than `none`) automatic replies won't be triggered.
[1]: https://www.rfc-editor.org/rfc/rfc3834.html
Signed-off-by: Gabriel Goller <g.goller@proxmox.com>
