In the past, I could add any email address that I own via Settings → Accounts → Add another email address you own.  I document this on my blog.  On that wzard, there were 2 options:But now it only lets you specify the SMTP server directly and it doesn't accept the standard settings of smtp.gmail.comDid they change policies?  Or am I missing something here?  I tried this on two different accounts.
Why does Gmail no longer offer the 'Send through Gmail option' for aliases?
gmail;smtp
Google is getting out of the business of sending email using domains that it does not administer, because it stands in the way of implementing rules that reduce spoofed email, such as DMARC.  This also has the side effect of encouraging customers to host their email domains with Google.Google is grandfathering existing email adddress configurations, but they are not allowing new email addresses to be added.Yahoo did something similar when they activated DMARC enforcement.  This made it harder to send email from mailing lists claiming to come from @yahoo.com, @aol.com, etc. .  AOL soon followed suit. See this PCWorld article for more on the fallout and reasoning.Update: There was no formal Google announcement about this policy change, but this support thread has an answer from a Google employee.Update 2015-03-17: Google appears to have restored this functionality, but only by configuring Gmail to use the authorized SMTP server for the domain.  In this configuration, Gmail is acting solely as an email client, submitting your emails to the server that is the MTA for the domain. This also means that Gmail has to store your SMTP password in plain text in order to pass it along to the server.