Mail stack

A "mail stack" refers to a collection of software components that work together to manage and process email messages. The mail stack typically includes:

1. Mail Transfer Agent (MTA): responsible for transferring email messages between mail servers. Examples include Postfix, Sendmail, and Exim.
2. Mail Delivery Agent (MDA): responsible for delivering email messages to the recipient's mailbox. Examples include Procmail, Maildrop, and Sieve.
3. Mail User Agent (MUA): responsible for allowing users to compose, send, and receive email messages. Examples include Microsoft Outlook, Mozilla Thunderbird, and Apple Mail.
4. Spam Filter: responsible for filtering out spam and junk email messages. Examples include SpamAssassin, ClamAV, and SpamFilter.
5. Virus Scanner: responsible for scanning email messages for viruses and malware. Examples include ClamAV, AVG, and McAfee.
6. Content Filter: responsible for filtering out unwanted content, such as explicit images or attachments. Examples include SpamAssassin, ClamAV, and Postfix.
7. Authentication Server: responsible for authenticating email users and verifying their identities. Examples include LDAP, Active Directory, and Kerberos.
8. DNS Server: responsible for resolving domain names to IP addresses and routing email messages to the correct mail server. Examples include BIND, PowerDNS, and Microsoft DNS.

The mail stack can be configured in various ways, depending on the specific requirements of the organization or individual. Some common configurations include:

• Simple Mail Transfer Protocol (SMTP): a basic configuration that uses SMTP to transfer email messages between mail servers.
• Post Office Protocol (POP): a configuration that uses POP to retrieve email messages from a mail server.
• Internet Message Access Protocol (IMAP): a configuration that uses IMAP to retrieve and manage email messages on a mail server.
• Microsoft Exchange: a proprietary configuration that uses Microsoft's Exchange Server to manage email, calendar, and contact information.

The mail stack is an essential component of modern email systems, and its configuration and management require a good understanding of email protocols, security, and best practices.