Gmail – Can not add Google Suite account to Normal Gmail’s “Send mail as”. Error 535-5.7.8 Username and Password not accepted

Alright, I figured one way to do this. In order for this to work you need an email account without an @gmail.com address. I used a Google Apps account, but another service provider's should be fine as well (e.g. @yahoo.com, @hotmail.com, etc.). The key is, that when you press the "Next Step" button in the "Add another email address you own", it must ask you the "Send mail through your SMTP server?" question. If it does not, you must use some other email provider.

Here are the steps:

1. Press the Send mail from another address button.
2. For the email address, enter in a non-gmail address that you own. It doesn't mater which one you choose, no one will see it. The only thing that is important is that you can access it.
3. Press Next Step.
4. Choose to Send through [domain.com] SMTP servers.
5. Enter in the credentials for the other gmail account you want to send as:
   • SMTP server: smtp.gmail.com
   • Username: example@gmail.com (the other gmail address you want to send as)
   • Password: (the password to login to the above gmail address)
   • Use SSL
   • Port: 465
6. Press Add Account
7. Verify the address by clicking on the link that was sent to you.
8. Send an email message, and choose to send it as that temporary account from step 2.

Even though you chose to send as the address from step 2, it will appear as the email address you chose from step 5. This is more of a temporary workaround, since this seems like a bug in Gmail, which may be fixed sometime in the future.

According to Google Support you can use the recovery link on this page: Recovering sign-in information

From here, you should try with all accounts you are associated with to see what accounts are linked. (Assuming you remember all email accounts used apart from the one you forgot). It is sort of hit and miss but it has worked for me on two separate occasions.

You should get an email similar to the following.

Your recovery address, phwd@gmail.com, is associated with:

xxxx@gmail.com
xxxx@gmail.com
xxxx@gmail.com
xxxx@gmail.com
xxxx@gmail.com

To sign in, visit the link below.

http://www.google.com/accounts/

If you've received this mail in error, it's likely that another user entered your email address by mistake while trying to recall their username. If you didn't initiate the request, you don't need to take any further action and can safely disregard this email.

If clicking the link above does not work, copy and paste the URL in a new browser window instead.

Thank you for using Google.

For questions or concerns regarding your account, please visit the Google Accounts FAQ at http://www.google.com/support/accounts/.

This is a post-only mailing. Replies to this message are not monitored or answered.

As seen above it works for multiple accounts. So any account that has phwd@gmail.com listed is brought up in the list.

Additionally you can search your email accounts for the following subject line

Your Gmail address has been created

This will bring up (if you didn't delete it), the confirmation email messages of all Gmail accounts you used the current account as a recovery point. Although, based on "used in ages" I am not sure how far back Google used to send out this message.