Why Won't My Email Client Connect?

If Outlook, Apple Mail, Thunderbird, or your phone cannot sign in or sync, start by copying the connection settings from Apps & devices. A wrong hostname, port, username, or password is much more common than a server problem.

Copy the connection settings from Apps & devices

Open Mailboxes, select the mailbox, then choose Apps & devices. Copy the hostname, port, and security option shown there. Those values are the source of truth for that mailbox.

For a standard domain, the usual platform hostnames above are expected. White Label accounts can also use branded client hostnames, but only after TrekMail verifies their DNS and certificates. Do not guess that imap.yourcompany.com or smtp.yourcompany.com will work just because the mailbox uses that domain.

If your client offers automatic setup, use the values it finds only when they match Apps & devices. See Setting Up Apple Mail or Setting Up Outlook for client-specific steps.

Check 1: Use the full email address as the username

Enter alice@yourcompany.com, not just alice. TrekMail authenticates IMAP and SMTP with the full mailbox address.

If your client has separate username and email address fields, enter the full mailbox address in both.

Check 2: Use the mailbox password

The Dashboard account password and a mailbox password are different. An email client needs the password for that specific mailbox.

If you need a new mailbox password, you can:

• Reset the mailbox password as the account owner from the Mailbox detail page in the dashboard.
• Have the mailbox user reset it themselves at the self-service password page.

After changing the password, update it in every mail app, phone, script, or device that uses this mailbox. An old saved password on one device can keep causing failed sign-in attempts.

Check 3: Match the hostname to Apps & devices

For most accounts, use these platform hostnames:

• IMAP: imap.trekmail.net
• SMTP: smtp.trekmail.net

If Apps & devices shows a branded IMAP or SMTP hostname, use that hostname instead. If the branded mail zone is not ready, the screen keeps showing the working platform hostname. The address after @ in your mailbox does not by itself determine the server hostname.

Check 4: Pair the port with the right security option

Choose 993 with SSL/TLS for IMAP. For SMTP, start with 465 with SSL/TLS. Use 587 with STARTTLS when port 465 is blocked.

Do not select No encryption. TrekMail does not accept unencrypted IMAP or SMTP connections.

Check 5: Rule out a network or VPN block

Some office networks, VPNs, and internet providers restrict mail ports. Port 25 is not supported for email-client sending, but an older client may still try to use it.

Try these checks in order:

1. Turn off a VPN temporarily, if your organisation permits it, and try again.
2. Try a different connection, such as a mobile hotspot.
3. Try port 587 with STARTTLS instead of port 465 with SSL/TLS.

If the connection works on another network, ask your IT team or provider to allow outbound access to the outgoing hostname shown in Apps & devices and the selected port. Do not use a fixed IP address from an old guide: the hostname is the supported setting.

You can use TrekMail webmail while the network issue is being resolved.

Check 6: Check for too many open IMAP connections

Each mailbox has a per-plan limit on concurrent IMAP connections, both per-IP and total. When you hit the cap, the IMAP server rejects new connections with "Maximum connections exceeded" or your client shows a generic "couldn't connect" error.

Common causes include:

• A client watches many folders for new mail.
• Opening the same mailbox in multiple clients on the same machine multiplies the count.
• Phones and desktop apps are both connected at the same time.

To reduce the number of connections:

• Close clients you're not actively using.
• Reduce the number of folders your client watches for new mail.
• Reopen the client after closing unneeded devices or sessions.
• Choose a plan with a higher connection limit if this mailbox genuinely needs more concurrent use.

Check 7: Check whether your plan allows sending

Nano accounts can receive mail but cannot send. If the client connects and receives messages but every outgoing message fails, move to Starter or a higher paid plan.

New and never-paid accounts can also have lower temporary safety limits than the limits shown for their plan. See Can't Send Emails for what to check before changing a plan.

Check 8: Check daily and hourly sending limits

If you can authenticate and send some messages but later sends are blocked:

These are maximum plan limits. Current safety limits can be lower for new or never-paid accounts. If the client reports that sending is temporarily limited, reduce the batch size and review Can't Send Emails. Do not assume the client will resend messages automatically.

Check 9: Check the mailbox, account, and domain status

Check that the mailbox is active in the Dashboard and that the account is not suspended. A temporary sending pause can stop outgoing mail without stopping incoming delivery. If a client cannot sign in at all, confirm the mailbox's status with the account owner or support.

For managed sending, the domain must have the required DNS records and be active in the Dashboard. DNS setup depends on whether the domain receives mail through TrekMail or is sending-only, so follow the record table for that domain instead of treating every missing record as the same problem. See Checking DNS Status.

Check 10: Remove an old saved profile carefully

If you moved from another provider, your client may still be using saved credentials or old server settings. First compare every field with Apps & devices. If the client still uses the old settings, remove that account profile and add it again with the current values. Make sure you know whether the client stores any local-only mail before removing a profile.

Common error messages decoded

Still stuck

Open a ticket from the Support page. Include:

• Your mailbox address (alice@yourcompany.com).
• The exact client (Outlook 365, Apple Mail 16.4, Thunderbird 115…).
• The exact error message your client shows.
• Whether you can reach TrekMail webmail with the same credentials (this confirms whether the password is right and the mailbox exists).

Do not include your password, a recovery code, or an access token in the ticket.