22. A system comprising: one or more hardware processors: and a memory storing instructions, operable when executed by the one or more hardware processors to cause the one or more hardware processors to perform operations including: determining that a user of a first instant messaging service is associated with a second instant messaging service different from the first instant messaging service; identifying user identities for users other than the user, wherein the user identities are associated with the first instant messaging service and the user identities are stored in a first list associated with the user; determining if at least one of the identified user identities associated with the first instant messaging service has a matching user identity associated with the second instant messaging service by identifying if a unique portion of the at least one of the identified user identities has a required amount of common features with a unique portion of the user identity associated with the second instant messaging service; determining a degree of uniqueness of an identified user identity; adjusting the required amount of common features between the unique portion of the identified user identity and the unique portion of a matching user identity associated with the second instant messaging service based on the determined degree of uniqueness of the identified user identity; and modifying a second list associated with the second instant messaging service to include the matching user identities.
22. A system comprising: one or more hardware processors: and a memory storing instructions, operable when executed by the one or more hardware processors to cause the one or more hardware processors to perform operations including: determining that a user of a first instant messaging service is associated with a second instant messaging service different from the first instant messaging service; identifying user identities for users other than the user, wherein the user identities are associated with the first instant messaging service and the user identities are stored in a first list associated with the user; determining if at least one of the identified user identities associated with the first instant messaging service has a matching user identity associated with the second instant messaging service by identifying if a unique portion of the at least one of the identified user identities has a required amount of common features with a unique portion of the user identity associated with the second instant messaging service; determining a degree of uniqueness of an identified user identity; adjusting the required amount of common features between the unique portion of the identified user identity and the unique portion of a matching user identity associated with the second instant messaging service based on the determined degree of uniqueness of the identified user identity; and modifying a second list associated with the second instant messaging service to include the matching user identities. 23. The system of claim 22 , wherein one or more of the user identities associated with the first instant messaging service comprise electronic mail addresses.