While Dovecot, Postfix, and Sendmail all handle email operations, they serve fundamentally different purposes in the mail delivery chain:

• Postfix/Sendmail: Pure MTA (Message Transfer Agent) focused on SMTP operations - sending/receiving mail between servers
• Dovecot: Primarily an MDA (Mail Delivery Agent) and IMAP/POP3 server - manages mailbox access and storage

The Unix philosophy of "do one thing well" applies perfectly here. A typical mail flow:

Incoming mail: 
Internet → Postfix (SMTP) → Dovecot (LMTP delivery) → Maildir storage

Outgoing mail:
MUA → Postfix (SMTP submission) → Internet

Mail access:
Dovecot (IMAP/POP3) ↔ Maildir storage

Performance Optimization

Postfix handles the CPU-intensive SMTP protocol processing while Dovecot specializes in efficient mailbox access:

# Postfix main.cf optimization for SMTP
smtpd_proxy_options = speed_adjust
smtpd_client_connection_count_limit = 20

Security Isolation

Running different components with separate privileges reduces attack surface:

# Example permissions for mail directory
/var/mail/vhosts:
- Owned by vmail:vmail (Dovecot runs as this user)
- Mode 770 (Postfix can write, Dovecot can read)

Protocol Specialization

• Postfix excels at SMTP (RFC 5321) with features like:
  • SPF/DKIM/DMARC verification
  • Greylisting
  • Rate limiting
• Dovecot specializes in IMAP (RFC 3501) with:
  • Full-text search
  • Compression
  • Push notifications

Here's a minimal working configuration for Postfix+Dovecot integration:

# Postfix main.cf
virtual_transport = lmtp:unix:private/dovecot-lmtp
virtual_mailbox_domains = mysql:/etc/postfix/mysql-virtual-domains.cf
virtual_mailbox_maps = mysql:/etc/postfix/mysql-virtual-mailboxes.cf

# Dovecot 10-master.conf
service lmtp {
  unix_listener /var/spool/postfix/private/dovecot-lmtp {
    mode = 0600
    user = postfix
    group = postfix
  }
}

Simple use cases where you only need:

• Postfix alone: Outbound mail relay or basic SMTP server
• Dovecot alone: IMAP server accessing existing mail storage

But for a complete mail server, the combined solution provides enterprise-grade features through specialization.

While Dovecot, Postfix, and Sendmail all handle email, they serve fundamentally different roles in the mail delivery chain:

# Postfix/Sendmail as MTA (Mail Transfer Agent)
1. Receives email via SMTP (port 25/587)
2. Routes email between servers
3. Handles queue management

# Dovecot as MDA/IMAP (Mail Delivery Agent)
1. Delivers mail to local mailboxes (MDA)
2. Provides IMAP/POP3 access (ports 143/993/110/995)
3. Manages mailbox storage and retrieval

The separation allows each daemon to specialize:

• Postfix/Sendmail optimize for SMTP transactions (EHLO, MAIL FROM, RCPT TO commands)
• Dovecot excels at IMAP commands (FETCH, STORE, SEARCH) and mailbox formats (mbox, Maildir)

Here's how they interact in a typical setup:

# Postfix main.cf snippet
virtual_transport = dovecot
dovecot_destination_recipient_limit = 1

# Dovecot 10-mail.conf
mail_location = maildir:~/Maildir

# Authentication integration
service auth {
  unix_listener /var/spool/postfix/private/auth {
    mode = 0660
    user = postfix
    group = postfix
  }
}

The separation creates security boundaries:

Dovecot's IMAP implementation outperforms alternatives when handling:

• Large mailboxes (100k+ messages)
• Concurrent connections (500+)
• Full-text search operations

Benchmark tests show Dovecot delivers 3-5x better IMAP search performance compared to Courier or Cyrus when properly tuned.

While all-in-one solutions exist (like Exim), they often:

1. Compromise on either SMTP or IMAP performance
2. Create single points of failure
3. Limit flexibility in security hardening

The Postfix+Dovecot combination has become the de facto standard for Linux mail servers precisely because it leverages the strengths of each component while maintaining clear separation of concerns.