Mail server migration with message synchronization

1. A system for migration of a mail server that includes a processor and physical storage, the system comprising:

a migration utility running on a target server and configured to acquire a list of message identifiers (IDs) of all messages that have already been migrated and that already exist on the target server, and to write a list of the IDs into a file,

wherein the message IDs are generated based on a file name where each message is stored, if available, otherwise, based on a message header, if available, otherwise, based on a hash of the corresponding message;

the migration utility configured to execute a command to import, to the target server, any remaining messages that have not yet been migrated, and store the remaining messages on the target server using (i) a mail server Application Programming Interface or (ii) directly onto the mail storage or (iii) using an IMAP protocol or (iv) using POP3 protocol;

a target mail server residing on the target server and connected to the migration utility and to a mail storage; and

an input of the migration module on the target server configured to connect to an output of the migration utility on a source server using a Remote Procedure Call (RPC) agent so that the migration utility can stream the messages to the migration module in a stateless manner,

wherein:

the migration module receives mail messages from the RPC agent and provides the messages to the input of the migration utility as soon as it receives them; and

the migration utility imports the mail messages on the target mail server.

2. The system of claim 1 , wherein the target mail server stores message onto the mail storage.

3. The system of claim 1 , wherein the target mail server has a different type from a source mail server residing on a source server.

4. A method for migration of a mail server, the method comprising:

launching a migrator module on a target server;

requesting, by the migrator module, message identifiers (IDs) of all messages that have already been migrated and exist on the target server, from a migration utility,

wherein the message IDs are generated based on a file name where each message is stored, if available, otherwise, based on a message header, if available, otherwise, based on a hash of the corresponding message;

receiving a message IDs file;

providing the message IDs file to a Remote Procedure Call (RPC) agent on a source server;

deploying a migration utility on the source server and running the migration utility in a backup mode so that the migration utility can stream the messages to the migrator module in a stateless manner;

receiving messages by a mail server on the source server;

on the target server, importing any remaining messages that have not yet been migrated, and storing the remaining messages on the target server using (i) a mail server Application Programming Interface or (ii) directly onto the mail storage or (iii) using an IMAP protocol or (iv) using POP3 protocol;

converting the messages into a server-specific format and providing the messages to the migration utility;

converting the messages into a server-independent binary format and sending the messages to the migrator module on the target server;

providing the messages to the migrator module on the target server; and

sending the messages to a target mail server by the migration utility on the target server.

5. The method of claim 4 , further comprising using IMAP to copy mail messages, if the mail server is not detected.