When I first set Thunderbird up, I tried to set up my Thunderbird email in Windows 7 using my primary Apple email alias XYZ@mac.com, and it didn't work. So I set Thunderbird up with my Apple ID email account ABC@mac.com and that worked. (note I never send email from the actual Apple ID email account, on any device). I then added an identity XYZ@mac.com in Thunderbird using my primary Apple email alias XYZ@mac.com, and was happily sending and receiving mail on that email address in Thunderbird, till I went back to my ipad and noticed the "Sent folder" in the iCloud mail app for the XYZ account (working under the ABC@mac Apple ID) wasn't picking up anything I was sending from Thunderbird. In Tbird Account Settings under Outbound SMTP it shows 2 identical servers, one marked as (default) for my Apple ID email account (ABC@mac.com) the other being my "Identity" account (XYZ@mac.com). Switching the default from one to the other doesn't seem to make a difference. Not to over-complicate things, but I also see this in my console (along with a lot of other errors: "Security Error: Content at moz-nullprincipal:{795fe982-093d-42fe-907e-1f29d9eb48ae} may not load or link to imap://ABC@imap.mail.me.com:993/fetch%3EUID%3E/Sent%20Messages%3E15023?header=filter&emitter=js&part=1.2&filename=original.jpg" That email came in with a simple JPEG on my ios devices but not in Thunderbird. Any help greatly appreciated.