Internal: Use fallback_user as email sender and set Reply-To to actual sender - refs #4283

[christianbeeznest]

No description provided.

[ywarnier]

Looks good to me. I'm not sure what the e-mail of the fallback user is, though (where is it configured?)

[ywarnier]

Although the code looks good, this doesn't seem to be what I would be expecting.

• There is no place/process where we suggest to update the fallback user's e-mail address.
• Sending with the sender's "reply-to" should not be the behavior by default (we should use the platform's address as reply-to, otherwise we encourage off-platform conversations, which we generally want to avoid)

So I'm not merging this PR for now. We need to discuss this more.

[christianbeeznest]

Closing in favor of a revised approach aligned with #4283.
We should not use fallback_user in SMTP headers. Instead:

From/Reply-To come from platform settings (default Reply-To = platform).

fallback_user is used only for internal DB associations (ownership/creator reassignment, neutral sender inside Chamilo).