Which file contains autocomplete suggestions for email address in Gmail, and can I clear it?
I had very similar problem. In addition to that sometimes the e-mail address of the recipient was "beautified" like that: 

Pawel Debski president bla bla something &lt;e-mail address>

What I found was that Google on his own created Google Contacts profile for me (https://contacts.google.com/) and than my e-mail clients on few devices started creating contacts there, often duplicated with different labels. Some of the labels corresponded to the circles in Google Plus profile, but some were created by various e-mail clients more or less randomly.

When I cleaned-up all the contacts there the problem was solved.