I totally get how frustrating it can be when emails and attachments start acting up. Let's try to sort this out. Firstly, it's worth checking your email filters and settings just in case something got tweaked accidentally. Also, make sure your customer's emails aren't landing in your spam or junk folder. If attachments are causing trouble, it might be a compatibility issue or a size limit problem. You can try asking your customer to send attachments in a different format or smaller sizes. Give these a shot, and hopefully, your email flow will get back on track.

Check your account in webmail, as the mail provider might have sent the messages to Spam/Junk, before mail is downloaded to TB. If that's the case, use webmail controls to whitelist or unblock senders, and add them to webmail contacts.

Note that POP accounts only download the Inbox, while IMAP setups download all subscribed folders.