re :I discovered that an email on the Comcast server, which I could view on my iPhone, was not downloaded to my Thunderbird inbox.

Possible reasons. If the iphone used pop and did not have settings to 'Leave message on server', then the email was downloaded to iphone and deleted off server. When Thunderbird downloaded all new mail from server Inbox to pop Inbox, the email was not downloaded because it did not exist - it was not on server. If email still accessible via iphone then forward it to yourself to put a copy back on the server in the inbox. Then in Thunderbird, use 'Get Messages' to download .

If the iphone used imap and moved that email to another folder, so no longer in 'Inbox', then when Thunderbird accessed server to download all new mail in Inbox, it could not see any email that was not in the Inbox, so could not download. In which case, logon to webmail account using a browser and move that email back into the 'Inbox', then in Thunderbird click on 'Get Messages'.

Thanks for your reply. My iPhone uses IMAP. I found the missing note in my iPhone Mail Inbox when I was glancing through it for some other reason. So the note was still in the Inbox on the server. I leave messages on the server for 10 days. I generally don't look at my mail via the iPhone/iPad unless I'm traveling and don't have my laptop with me. So I generally wouldn't discover these missing notes. I've had other occasions where I find out someone has sent a note to a group I'm in only when I get a copy of the reply someone else in the group sends (I can see my name in the original distribution list but had never seen the first note.) Of course, I don't know how often this happens because I've only caught it in random circumstances. But I hope it isn't often. Perhaps related to this phenomenon is that sometimes, T-bird will present me with a new mail that shows it actually hit the inbox on the server several hours earlier. Now that I think about it, that seems to have stopped happening so that's a good thing. But it's another example of odd downloading I've experienced.

right click the inbox and select properties and then repair. Does the missing mail appear?

Thanks for the suggestion. Unfortunately, the missing email had cycled off of the server so it didn't appear. But I'll try it the next time I have the issue (and maybe periodically just to see if something new pops up.)