I use this technique to get multiple (over 50) emails to my primary GMail Email address
What you need is
1) A Primary Gmail Account
2) Multiple Secondary Gmail Addresses
3) Domains hosted on a CPanel or other admin tool that allows you to setup POP Accounts (actual email accounts using SMTP)
Gmail has a really cool POP fetch feature that allows you the retrieve upto 5 POP email addresses
What I have done is the following
1) for each domain i have registered a Gmail account
As a general rule i goto www(dot)grc.com/password.html and generate a random password and cut and paste part of the password as my Gmail Login for that email address and store it offline on my laptop
In CPanel I have created 5 email POP email boxes for each domain
do the same for domain2.com, domain3.com, etc ....
Log into the relevant Gmail Account and Setup the POP account - by filling in the username, password and SMTP for the pop addresses for each of the 5 POPS, you can then select to delete the email from POP or leave on the hosting box - I have chosen to delete the emails from my POP box
And forward that email address eg) domain.1(at)gmail.com -> to your primary email address (do the same for all the other gmail addresses)
What Gmail will do is in the domain.1(at)gmail.com account will periodically retrieve the emails by visiting the POP box and once its recieved will automatically forward that email/s to your primary account
The advantage here is you have backups and redundancy and instant reciept of all your email's
Now you can do that for all your domains. I use random passwords generated by CPanel for each POP
Now once that is completed (gets easier) I login into my Primary Gmail Address and in settings i can now configure that account to send from another email address.
To put it in simpler terms - My primary Gmail can recieve and send from all my email addresses as that email address from one place
Once this is done i have a Backup Primary email address that gets a copy of all my Primary Emails
If anyone is interested in more details i will find the google instructions and post them here for you
Happy Friday ...