Question 1

What does this IMAP test check?

Accepted Answer

This tool connects to your IMAP server on the selected ports (143, 993), tests TCP connectivity, checks STARTTLS or implicit TLS support, examines TLS version and cipher suite, validates the server certificate, and reads the server's CAPABILITY list.

Question 2

What is the difference between ports 143 and 993?

Accepted Answer

Port 143 is the standard IMAP port using STARTTLS to upgrade to encryption after connecting. Port 993 uses implicit TLS (IMAPS), where the connection is encrypted from the start. Most mail servers support both.

Question 3

What are IMAP capabilities?

Accepted Answer

IMAP capabilities are features the server advertises it supports, like IDLE (push notifications), MOVE, COMPRESS, QUOTA, and various authentication methods. The CAPABILITY command reveals what extensions are available for email clients to use.

Question 4

What is the difference between IMAP and POP3?

Accepted Answer

IMAP keeps your mail on the server and syncs it across every device — folders, read state, and all — so your mailbox looks the same on your phone and laptop. POP3 is the older protocol that downloads messages to one device and, by default, removes them from the server, so mail doesn't stay in sync. IMAP is the right choice for anyone reading mail on more than one device.

Question 5

Should I use port 143 or 993 for IMAP?

Accepted Answer

Prefer port 993, which encrypts the connection with implicit TLS from the start and is the recommended default (RFC 8314). Port 143 is fine only when the client immediately issues STARTTLS to upgrade to TLS before logging in — plain IMAP on 143 with no encryption sends your credentials and mail in the clear and should never be used across a network. This tool shows which form of TLS each port offered.

Question 6

Why won't my email client connect to the IMAP server?

Accepted Answer

The usual causes are a firewall blocking port 143 or 993, the wrong server hostname, the service not listening, or a TLS handshake that fails because of a bad or mismatched certificate. This tool connects from the public internet and reports the connection result, the TLS handshake, and any certificate problem separately, so you can tell a network block apart from a TLS fault.

Question 7

What does a certificate error on my IMAP server mean?

Accepted Answer

Mail clients verify the server's TLS certificate before logging in, so an expired, self-signed, or hostname-mismatched certificate makes clients warn the user or refuse to connect outright. The certificate's subject must match the hostname clients use to reach the server, it must be issued by a trusted CA, and it must be current. This tool reports the certificate's subject, issuer, expiry, and whether it's self-signed.