Hi, I've recently switched hosting providers (to Hostinger) and also started using Thunderbird (as it offered a better way to transfer emails across from previous provided and have them in same email client). Since doing that, my sent emails are continually getting blocked (marked as spam) and I have to contact Hostinger support to "unblock" my account. They've done some investigation and suggested that it is something to do with the email Header (they actually said a "missing header"). I've compared what is generated in the header when using the Hostinger webmail vs Thunderbird for Android, and one obvious difference is that there is no '''X-Sender''' in the Thunderbird for Android header (it also not present when using Desktop client) Could this be the cause of the issue? I can't locate where I can ensure X-Sender is included in the Header. Is there anything else I can check? Thanks