Which file contains autocomplete suggestions for email address in Gmail, and can I clear it? When I compose a new message in Gmail on my Android phone I'm offered several suggestions for the recipient (i.e. for the email's To: field) via an autocomplete function. These are often very old/unknown contacts which I'd like to no longer see as autocomplete suggestions, but I can't yet work out how to clear this list.

The contacts suggested appear to have come from an old list of "Other" contacts, i.e. people that I've contacted infrequently and who were not actual contacts that I ever added to my contact list. These only show up when I compose a new message in Gmail on my phone, and the autocomplete works as expected when on a non-Android device (laptop). My list of "Other" contacts have been wiped clean in my Google account, but after a sync I still get these autocomplete suggestions in Gmail on the phone. I get no such misbehavior when I compose an email in Gmail through Chrome on my laptop.

I've tried all manner of account syncs, remove and restore my account, clear data and cache of the Contacts and Gmail apps, reinstall factory versions of those apps, etc., all to no avail. I know enough Linux that I'm not too scared of getting into the filesystem and monkeying about, but not so much that I don't feel the need to ask for help from experts who might help keep me from bricking my phone. 

My hunch/assumption is that the Android Gmail autocomplete function is reading these outdated contacts from a list stored somewhere in a file on my phone which is impervious to the contact sync process or somehow not being cleared as expected otherwise.

My idea is to somehow search Android's filesystem for a file that contains the unwanted contacts and if found then wipe that file clean. Is this reasonable, and if so can anyone suggest guidance that'll make this less of a wild goose chase?

My phone details:

Model: Nexus 5X
Android version: 7.1.2
Baseband version: M8994F-2.6.37.2.21
Kernel version: 3.10.73-ge570678
Build version: N2G47F
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.