Some customers experience issues where e-mail subject lines are displayed incorrectly or missing in certain e-mail clients (for example, Apple Mail).
This happens when an invisible or non-printable character (such as a zero-width space or soft return) is accidentally placed at the end of the subject line.

Deployteq currently treats these characters as special characters, which causes the subject to be MIME-encoded (e.g.
=?UTF-8?B?c2Vpem9lbuKAqA==?=).
While this encoding is technically correct, it leads to problems in some e-mail clients that cannot properly decode these characters.

To prevent this, it would be helpful if Deployteq could:

Automatically detect and remove invisible or non-printable characters in subject lines, or

Show a warning message in the editor when such characters are present, alerting the user before sending.

This would help users avoid encoding-related issues and ensure that subject lines are displayed correctly across all mail clients.