Today I received an email with (raw) subject line

Subject: =?UTF-8?B?8J+Pi++4jw==?= A SALE to boost your
 =?UTF-8?Q?workout=0D=0A?=

When displayed in Emacs in either unthreaded or tree mode, “^M” appears after the word “workout”, and the displayed line is split into two, like this:

 Today 07:12  Jabra                🏋️ A SALE to boost your workout^M
                       (important inbox)

It would probably be a good idea to check for, and remove, carriage return characters in the subject line.

(Note that the message displays fine in the default threaded mode.)

Richard Stanton