(Simple Mail Transfer Protocol - Mail Transport Agent & Structured Query Language Databases)
SMTP MTAs are used to send and receive email messages to and from other SMTP MTAs.
An SMTP MTA is an email server itself and is capable of storing messages locally as a final destination. When used as a final destination for messages, it will usually function along side a POP and IMAP server which is used to extract the messages from the MTA and into an email client such as Microsoft Outlook or Mozilla Thunderbird.
SQL databases are databases that store information in a structured way so the data held within them can be retrieved quickly and efficiently as well as providing a way to avoid duplication thus helping to keep their size to a minimum.