1. A computer-implemented method, comprising: receiving, at a computing system and as having been sent by a first remote computing device, an electronic message that includes a username but does not include information that fully identifies a recipient for the electronic message; identifying, by the computing system, multiple domains for which the username may be valid, including a first domain and a second domain; querying, by the computing system, the first domain to determine that the username in the electronic message is not a valid username for the first domain; querying, by the computing system, the second domain to determine that the username in the electronic message is a valid username for the second domain; selecting, by the computing system and based on having determined that the username in the electronic message is not a valid username for the first domain but is a valid username for the second domain, to transmit the electronic message to a user account that is associated with the username and the second domain; identifying, by the computing system, a second remote computing device that is associated with the user account and to which the electronic message is to be transmitted; modifying, by the computing system and before the electronic message is transmitted to the second remote computing device, the electronic message to add the second domain into the electronic message, so that the electronic message includes information that fully identifies the recipient for the electronic message; and transmitting, by the computing system as a result of having selected to transmit the electronic message to the user account, the electronic message that has been modified to include the second domain to the second remote computing device that is associated with the user account.
1. A computer-implemented method, comprising: receiving, at a computing system and as having been sent by a first remote computing device, an electronic message that includes a username but does not include information that fully identifies a recipient for the electronic message; identifying, by the computing system, multiple domains for which the username may be valid, including a first domain and a second domain; querying, by the computing system, the first domain to determine that the username in the electronic message is not a valid username for the first domain; querying, by the computing system, the second domain to determine that the username in the electronic message is a valid username for the second domain; selecting, by the computing system and based on having determined that the username in the electronic message is not a valid username for the first domain but is a valid username for the second domain, to transmit the electronic message to a user account that is associated with the username and the second domain; identifying, by the computing system, a second remote computing device that is associated with the user account and to which the electronic message is to be transmitted; modifying, by the computing system and before the electronic message is transmitted to the second remote computing device, the electronic message to add the second domain into the electronic message, so that the electronic message includes information that fully identifies the recipient for the electronic message; and transmitting, by the computing system as a result of having selected to transmit the electronic message to the user account, the electronic message that has been modified to include the second domain to the second remote computing device that is associated with the user account. 5. The computer-implemented method of claim 1 , wherein an author of the electronic message has not specified that the recipient for the electronic message is the user account.