What is the outgoing server name for the account(s) you're sending on, e.g. smtp.office365.com or smtp.mail.yahoo.com?

Outgoing Server Name: AT&T-outbound.att.net

So it's the yahoo servers again.

Does this occur when replying to an email or sending a new email?

Menu app icon > Options > Options > Display > 'Formatting' tab click on 'Advanced' button to show 'Fonts & Encoding' What is the default 'Text Encoding' for Outgoing Mail?

Are you able to find out what the recipient is using for 'Text Encoding' for incoming mail?

Try this: Menu app icon > Options > Options > Advanced > 'General' tab click on 'Config Editor' button accept the risk In search type: mime Look for this line: mail.strictly_mime Is it set to 'false' ? double click on that line to toggle the value to 'True'.

Close the window top right X

Please report back on results.

No, I am not able to find what the recipient is using for 'Text Encoding' for incoming mail.

I just followed your instructions.  I will let you if it works.  In the example of junk symbols I posted here, I had used my spacebar a lot in the e-mail, instead of pressing the Enter key to avoid double spacing paragraphs.  Most of the time, the junk appears in spaces between sentences & maybe between words as well.

Have a look at this

http://forums.mozillazine.org/viewtopic.php?p=14830516#p14830516

Go to the Configuration Editor (Tools, Options, Advanced, General, Config Editor). Scroll down to

mail.strictly_mime

Click on it to change it from False to TRUE.

I had the same issue with yahoo, though not to the same extent as the posting you have shown

Thank you! So far, so good.