Some email recipients get messages with =0D or =3D characters

Question

I have a LAMP web application that emails users. Some users have complained that instead of seeing html email messages, they see weird sequences of characters such as =0D o

Answer 1

This is called quoted printable encoding. Some system that handles the mail while it is being delivered to the recipients that are seeing the offending characters messes up the encoding or the header information about the encoding.

Check whether the encoding you are setting when sending the mail matches what you are writing to the mail and whether that is also what is received by other people.