I have about 4 emails in my inbox that say "no sender". They don't delete when you select them and click "Delete".
Thanks

I just mark them as junk. Eventually (hopefully) they'll go to junk automatically.

There's a very good chance that these are corrupt messages.

The usual fix is to rebuild the mailbox from the "Mailbox" menu, and if that doesn't work then pulling the envelope index files will usually do the trick.

However, there's some risk to this as multiple corrupt messages can point to serious corruption and some otherwise intact messages may vanish after a rebuild with that kind of corruption. Make sure that your backups are up to date before trying either of these methods.

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login to your webmail and delete them from there

I have been getting a bunch of those lately. They have a button that says "Remove Me" which looks like an attempt to collect live addresses so I just delete them.