A message transfer agent (MTA) is a software application or computer programused within an Internet message handling system (MHS) that transmits emails between the computer equipment of a person who sends and another receiving.
It is responsible for the transfer and route of an email message from the source computer to the arrival computer. The main support of an MTA is an exchange system with client/server architecture.
An MTA is also known as a mail relay.
An MTA is responsible for the main tasks concerning email delivery; these functions include:
An MTA also includes features for handling incoming email, such as replies to be sent and messages bounced remotely.
An MTA is just one part of the entire email delivery process. It gets an email from the mail delivery agent, who, in turn, receives it from the mail user agent (MUA). The MUA is commonly known as an email client, a program or software that is used to handle email-related matters.
When the MTA receives the email, the relay kicks in. The email can be forwarded to other MTAs if the recipient is not hosted locally. Then it is the turn of the mail delivery agent (MDA). This is the last stage of the email before it is delivered to the recipient's mailbox. The sending of email is done through SMTP (or extended SMTP), and for the last stage (MDA to MUA), POP3 or IMAP4 is used.
In summary, MTAs do the following:
In most cases, MTAs employ a store-and-forward form of mail management, which means that outgoing mail is queued and waits for a response from the receiving server. An MTA will try to send emails repeatedly. If the mail is not delivered within the established period, it will be returned to the mail client.
It cannot be said that on-premises MTAs are entirely better than any cloud-based email infrastructure, as each specific project has its own unique needs and can benefit from a cloud-based solution.
On-site mail transfer agents are the primary choice for businesses and large businesses. This brings with it a complete email infrastructure that can be configured according to requirements.
When you don't have a significant amount of financial resources and your email sending needs are moderate, then you can consider the option of a cloud-based SMTP relay service (Mailgun or SendGrid). It's a quick and helpful answer to get started. The main disadvantage is that it is a shared service. You do not have control of everything, and the infrastructure is shared with others (although some services have dedicated IP optionally).