The issue occurs when you use the POP3 adapter with POP3 mail servers that add a base64-encoded "Content-Description:" MIME header field to the MIME of emails with attachments. In some languages, attachments that have long names will cause the following error:
There was a failure executing the receive pipeline: "Microsoft.BizTalk.DefaultPipelines.PassThruReceive, Microsoft.BizTalk.DefaultPipelines, Version=3.0.1.0, Culture=neutral, PublicKeyToken=TokenID" Source: "Unknown " Receive Port: "ReceivePortPOP3" URI: "POP3://outlook.office365.com#EmailID" Reason: 0x8007005
After that, the POP3 adapter will stop receiving emails.