Keep in mind that all file attachments are sent as encoded ASCII anyway, and turning them into attachments is a two stage process: It's up to the sending computer's mail software to put the correct identifiers and encode the ASCII data correctly, and it's up to the receiving computer to correctly decode those headers and data.
One of those two things has gone wrong. Perhaps because of some setting.
I was going to say it was the sending computer's method of encoding and sending the file. But then you said others have been receiving the messages OK. Still, perhaps the sender changed the encoding method and the others who are receiving the messages OK are using a different piece of mail software than you are.
Let me clarify the symptoms:
- Only email attachments from one sender are coming up as ASCII for you.
- Those same troublesome emails are received fine by other people.
- Emails from other senders with file attachments are coming up fine for you.
Is that correct?
It would be helpful to know the names of the email client software being used in the case of the sender, you, and one of the receivers who gets the emails fine.