Do I need Autoconfig if I use Exchange?

Not for Outlook, which uses Autodiscover (a separate tool). Autoconfig is the way for Thunderbird, Apple Mail, K-9 Mail and similar clients, also against an Exchange server with IMAP/SMTP.

How do I create an autoconfig XML?

Create a config-v1.1.xml following the Mozilla clientConfig schema, with one incomingServer (imap or pop3) and one outgoingServer (smtp) each with hostname, port, socketType and authentication. Serve the file over HTTPS at autoconfig. /mail/config-v1.1.xml and set the DNS entry autoconfig. .

What does an SRV record with a target of '.' mean?

Per RFC 6186, '0 .' means this service (for example unencrypted IMAP) is explicitly not offered. That is a valid, sensible entry, not an error.

Is one of the three methods enough?

Yes. A maintained autoconfig XML satisfies most clients. SRV records are a lean alternative. If the domain is in the Mozilla ISPDB, it even works without entries of your own. But multiple ways must not contradict each other.

Which ports go with which socket type?

SSL/TLS from the start: IMAP 993, POP3 995, SMTP 465. STARTTLS on the plain-text port: IMAP 143, POP3 110, SMTP 587. Port 25 is the server-to-server port and unsuitable for clients.

Why is the certificate of the IMAP/SMTP servers not checked?

This tool checks what the domain publishes and whether the named hosts resolve. The connection and certificate test of the servers is a separate tool.

Autoconfig Check

Check Thunderbird auto-configuration: SRV records, autoconfig XML and the Mozilla ISPDB.

Thunderbird, Apple Mail, K-9 Mail and many other clients set up a mailbox from the email address alone if the domain publishes the right information. If that does not work, the user has to enter server names, ports and encryption by hand, a common source of support requests. This check inspects the three ways a client without prior knowledge tries in turn.

What this tool checks

First, SRV records per RFC 6186: _imap._tcp, _imaps._tcp, _pop3._tcp, _pop3s._tcp, _submission._tcp and _submissions._tcp name the target host and port per service. A target of . means the service is deliberately not offered. The port is checked against the service. Second, the autoconfig XML from autoconfig.<domain>/mail/config-v1.1.xml and <domain>/.well-known/autoconfig/mail/config-v1.1.xml: it describes IMAP, POP3 and SMTP servers with host name, port, socket type (SSL/STARTTLS/plain) and authentication method. Third, the Mozilla ISPDB at autoconfig.thunderbird.net: if the domain is listed there, Thunderbird finds the servers even without entries of its own.

Reading the result

Green means: at least one of the three ways provides a complete, encrypted configuration without a contradiction. Warnings appear for plain as the socket type (unencrypted login), for a port that does not match the socket type (for example STARTTLS on 993), for hosts that do not resolve, and for contradictions between SRV and XML. If none of the three ways finds anything, that is a warning: the client then falls back to guessing (imap.<domain>, mail.<domain> and similar).

Background

The SRV records for mail clients are defined by RFC 6186, the general SRV format by RFC 2782. The autoconfig XML is a Mozilla format (clientConfig / config-v1.1.xml), not an RFC standard, but it is also read by other clients. The ISPDB is Mozilla's central collection of such configurations for known providers. The certificate and connection test of the named IMAP and SMTP hosts is deliberately not part of this check, which inspects what the domain publishes.

Common problems and how to fix them

The client does not set up automatically at all. None of the three ways is present. The simplest is the autoconfig XML: put the file at autoconfig.<domain>/mail/config-v1.1.xml (HTTPS, Content-Type text/xml or application/xml) and create autoconfig.<domain> in DNS.
The autoconfig XML names plain. The client would send credentials unencrypted. Switch to SSL (IMAP 993, SMTP 465) or STARTTLS (IMAP 143, SMTP 587).
SRV and XML contradict each other. Client behaviour then becomes unpredictable. Bring both sources to the same host name and the same ports, or drop one of the two.
Wrong port for the socket type. SSL belongs on 993 or 465, STARTTLS on 143 or 587. An SSL entry on port 143 does not connect.
Domain is in the ISPDB with outdated data. This mainly affects domains that used to be with a different provider. Submit a correction to the ISPDB at Mozilla and also provide your own autoconfig XML, which takes local precedence.

Common questions

Do I need Autoconfig if I use Exchange?: Not for Outlook, which uses Autodiscover (a separate tool). Autoconfig is the way for Thunderbird, Apple Mail, K-9 Mail and similar clients, also against an Exchange server with IMAP/SMTP.
How do I create an autoconfig XML?: Create a config-v1.1.xml following the Mozilla clientConfig schema, with one incomingServer (imap or pop3) and one outgoingServer (smtp) each with hostname, port, socketType and authentication. Serve the file over HTTPS at autoconfig.<domain>/mail/config-v1.1.xml and set the DNS entry autoconfig.<domain>.
What does an SRV record with a target of '.' mean?: Per RFC 6186, '0 .' means this service (for example unencrypted IMAP) is explicitly not offered. That is a valid, sensible entry, not an error.
Is one of the three methods enough?: Yes. A maintained autoconfig XML satisfies most clients. SRV records are a lean alternative. If the domain is in the Mozilla ISPDB, it even works without entries of your own. But multiple ways must not contradict each other.
Which ports go with which socket type?: SSL/TLS from the start: IMAP 993, POP3 995, SMTP 465. STARTTLS on the plain-text port: IMAP 143, POP3 110, SMTP 587. Port 25 is the server-to-server port and unsuitable for clients.
Why is the certificate of the IMAP/SMTP servers not checked?: This tool checks what the domain publishes and whether the named hosts resolve. The connection and certificate test of the servers is a separate tool.