I use one central email address: email@example.com (email anonymized). I want to add my work address firstname.lastname@example.org to my primary address so I can control it from there.
option1: gmail's pop3 importer
Gmail cannot use IMAP to download messages (or I haven't found out how) from other mail servers. It can use POP3:
What i prefer is to make the mail server at fake.company.com to forward all the messages to email@example.com. This depends from server to server.
If you want to pose as firstname.lastname@example.org from email@example.com, you have to use fake.company's email servers, here's how it's done:
On firstname.lastname@example.org's settings, do:
Gmail -> settings -> accounts -> Add another email address you own
Then add the info of email@example.com:
NOTE: Uncheck "Treat as an alias"
Then add the server info:
Then an email with a code will be sent to firstname.lastname@example.org
Give the code to gmail:
Now we're ready, compose a new email and put a different FROM address:
Now when you receive an email to email@example.com designated for firstname.lastname@example.org and you click reply, gmail will automatically put email@example.com as the FROM address.
NOTE: People on the other side will never know you use firstname.lastname@example.org.