Mail server resembles a computer connected within a network which performs function similar to Post office virtually. Email- server contains a storage place were emails are stored for local clients. Once the email gets added to the storage area, pre-defined rules are added in accordance to determine the path mail server should consider while transferring specific message to the destination. Mail servers are of two main categories: Outgoing mail servers and incoming mail servers. Outgoing mail are transferred through SMTP protocol and incoming mails are delivered through POP3 or IMAP protocols
SMTP refers to Simple Mail Transfer Protocol. It used to deliver mails to particular destination over Internet. SMTP is referred to transporting outgoing emails to particular destination. SMTP verifies the configuration and grants the permission to a computer that is making an attempt to send a message. It sends the message to the specified destination and also tracks it to see whether the message has been delivered successfully or not. If the message is not delivered successfully then an error message is send to the sender.
MTA refers to Message Transfer Agent or Mail Transfer Agent. It is responsible for transferring and routing an Electronic-mail message from the sender’s computer to the recipient’s computer. Most probably, MTA receives emails from other MTA. A message transfer agent receives incoming emails and forwards the messages to individual clients/users. The main function of the MTA is forwarding the incoming message to the perfect end-user or destination. Microsoft Exchange and UNIX sendmail are good examples of MTAs.