How are you retrieving the sender email address? Are you working with
Exchange server? You might be getting an Exchange distinguished name email
address which is in the form usually of something like a bunch of "o=",
"ou=" and "cn=" tags.

Same question for your other post, sending using an Exchange account will
not have a sender email address in the sent email, but you can retrieve the
address from parsing the information from the PR_SENDER_ENTRYID property,
which when converted into a text string has the distinguished name address.

In addition to whether or not you're using Exchange you also need to tell us
what Outlook version you're using and what language you're using for your
code.