Settings that work.

Username: <username>@gmail.com
IMAP: imap.gmail.com - SSL (port 993)
POP: pop.gmail.com - SSL (port 995)

smtp: smtp.gmail.com - SSL (port 465) or TLS/STARTTLS (port 587) - user
authentication needed

Pop & Imap when first connecting may return a dialog box pointing to the following url.

https://support.google.com/mail/accounts/answer/78754

Visit the url and click 'allow less secure account' this is not that big of a deal considering
what other apps that also fall into this category which are listed below:

• The Mail app on iPhone or iPad with iOS 6 or below,
• The Mail app on your Windows phone preceding the 8.1 release,
• Some Desktop mail clients like Microsoft Outlook and Mozilla Thunderbird

Click on allow less secure account again and then click 'turn on'

Now gmail in seamonkey either pop or imap should work just fine.