Mail servers

Viauna uses only standard IMAP and SMTP, so it should work with any compliant server. It is developed and tested against Dovecot, the IMAP server inside Mailu, mailcow and docker-mailserver.

What the server needs

• IMAP over TLS (993) or STARTTLS (143).
• SMTP submission with authentication, over TLS (465) or STARTTLS (587), accepting the same login as IMAP. Each message is sent with the signed-in person's own password.
• A Sent folder. Viauna files a copy of each sent message there itself, as most IMAP servers expect.
• For labels: custom keywords (PERMANENTFLAGS \*). Dovecot, Cyrus, Stalwart and most others allow them. Folders work either way.

CONDSTORE/QRESYNC, MOVE, UIDPLUS, SPECIAL-USE and IDLE are used when the server offers them, with fallbacks when it doesn't.

Each mailbox in use holds three IMAP connections from Viauna, and logs in briefly about every 10 minutes to check its password again. See How it works: Mail sync.

For filters and the vacation responder: ManageSieve, usually port 4190. See Filters and vacation.

Search runs on the server. A full-text search plugin (Dovecot's fts-flatcurve or fts-xapian, for example) keeps searches of message bodies fast on large mailboxes.

Connecting over a Docker network

When Viauna runs next to your mail server, connect over the shared Docker network, and check the certificate against the public hostname:

IMAP_HOST: dovecot                      # the mail container's name on the network
IMAP_TLS_SERVERNAME: mail.example.com   # the name on its certificate
SMTP_HOST: postfix
SMTP_TLS_SERVERNAME: mail.example.com

Logins through Viauna come from one address

Your mail server sees every sign-in made through Viauna as coming from Viauna's own address. If it blocks addresses after failed logins (Mailu's AUTH_RATELIMIT_IP, or fail2ban watching Dovecot), a few mistyped passwords, or one attacker, can lock out everyone who uses Viauna. Exempt Viauna's address there. Viauna applies its own limits to the real client addresses instead: 20 attempts per address and 8 per login every 15 minutes, with TRUST_PROXY on so it can see those addresses.

Tested with

Server	Status
Dovecot 2.3	Tested: the development and CI server
Mailu 2024.06	Tested; see Mailu
mailcow, docker-mailserver	Dovecot inside, so expected to work; not yet tested
Stalwart, Cyrus	Expected to work; not yet tested

Running Viauna with another server? Please tell us how it went, whether it worked or not.

Hosted mailboxes

Viauna can sign in to a hosted mailbox that offers IMAP and SMTP with a password or an app password: point IMAP_HOST and SMTP_HOST at the provider, or turn on ALLOW_CUSTOM_SERVERS so people can enter their own.

• Gmail isn't a target: its IMAP works differently (it files its own copy of sent mail, and its labels are folders).
• Providers that require OAuth sign-in, such as Outlook.com, don't work yet.