The INBOX.msf file in the Thunderbird profile is only an index file of the INBOX folder. The INBOX messages are stored in the INBOX file in the profile. Did you verify if those missing messages are still displayed on the webmail page of your email provider? Do you use the same email address in another email client on another support such as PC or smartphone?

Thanks for your reply.

To answer your queries:

No, the missing messages are not still displayed on the webmail page of my email provider--which is Mail.com. Does this suggest that the problem lies with Mail.com?

I use this email address only with Mail.com. I use TB to manage my email on a desktop and on a laptop. I use the Mail.com app to access and manage my email on my phone.

If this is an IMAP account and the missing messages are no longer visible on the webmail page they are lost, unless your email service provider is able to retrieve them. But I can't say who's fault it is since I'm a bit troubled by your answer:

I use this email address only with Mail.com. I use TB to manage my email on a desktop and on a laptop. I use the Mail.com app to access and manage my email on my phone.

Tell me if I'm wrong: you use this same @mail.com address on a desktop and a laptop PC and on your smartphone. And is this same address set up as an IMAP account on all devices? Are the missing messages still visible on one of those other devices?

Thanks again. The email address I use with Mail.com is an *@earthling.net address that I purchase from them.

The inbox at Mail.com is identical to the inbox on TB--1814 emails dated 1/4/2024 to today--with a gap of no emails from 12/4/2025 to 3/12/2026.

I presume incoming emails to that earthling.net address reach Mail.com and then are retrieved by TB each time I check TB on any of my three devices. It would appear that the no email gap came about at Mail.com since their server has emails both before and after the gap. And this in turn resulted in the same gap in the TB INBOX files. Is that logical?

TB accounts on both my laptop and desktop are set up as IMAP: imap.mail.com. I believe the TB account on the Mail.com app on my phone is the same, however I cannot find settings specific to the app.

One possible plus in this situation is that I have not used my desktop since late January as I am traveling. I will get back to that computer around April 10. I presume the TB INBOX files on the desktop are still valid through it's last use in late January. If I open TB without being connected to the internet, the emails through late January should still be there and retrievable--again, is that logical?

I will ask Mail.com if they can retrieve the missing emails, but I suspect that's not possible, as you say.

One possible plus in this situation is that I have not used my desktop since late January as I am traveling. I will get back to that computer around April 10. I presume the TB INBOX files on the desktop are still valid through it's last use in late January. If I open TB without being connected to the internet, the emails through late January should still be there and retrievable--again, is that logical?

It is logical. If on your desktop PC in Account Settings > Synchronisation & Storage the option "Keep messages in all folders for this account on this computer" is checked (which is a Thunderbird default) and if you start in offline modus you should see the missing messages. Create a folder in Local Folders and copy all those messages to this folder so that they will be safe when you go online.

I'm pretty sure the "Keep messages in all folders . . ." option is checked on my desktop. I know it is on the laptop.

Any suggestion on how to avoid this situation in the future? Would periodically creating a backup copy of the TB INBOX files make sense? If I have automatic backup of my hard drives to the cloud, should good copies of these files be available there? I suppose they would get overwritten each time there is an automatic backup.

Data backups are the best way to prevent data loss. Automatic backups of data on your hard drives would include your Thunderbird data which are stored in the Thunderbird profile. You also should be able to copy them back from the cloud. As far as I know automatic backups are incremental backups.

OK--thanks for all your help on this.