If your company has merged with another company, or if your company is changing its name then here is how you get multiple email addresses.
Define a Global Domain Document, mention your primary Internet domain and also define your alternate Internet domains.(These alternate domains will act as an alias for your primary Internet domain.)
This configuration can be defined from Servers - Domains view of Domino Directory. Make sure that all your alternate domains are configured to send and receive Internet emails.
For example if your e-mail id is firstname.lastname@example.org, If your company Acme has changed its name to AcmeCorp, then you get email@example.com.
Also if AcmeCorp acquires ChairCreations Inc, whose Internet domain is chaircreations.com, then you get an additional email Id of firstname.lastname@example.org.
In the above example Acme is the primary Internet Domain, whereas acmecorp, chaircreations are the alternate Internet Domains for Acme.
So you end up with these may email addresses.
email@example.com firstname.lastname@example.org email@example.com firstname.lastname@example.org email@example.com firstname.lastname@example.org