Connect Microsoft 365 to Mailbind

Microsoft 365 IMAP and SMTP settings

The username is the full mailbox address. These are the values Microsoft publishes for Exchange Online; note that the outgoing host differs from the one Outlook.com uses.

Security defaults and basic authentication

Microsoft documents two tenant-level settings that decide whether any IMAP client can connect. Security defaults, if enabled for your organisation, automatically disable POP3 and IMAP4 in Exchange Online. Separately, Microsoft advises organisations to disable basic authentication to protect against password-spray attacks, and notes that doing so blocks legacy protocols including POP and IMAP.

That is not a Mailbind limitation and no setting on our side changes it. If your tenant has disabled basic authentication, the way in is OAuth: use “Continue with Microsoft” on the connect screen, which asks Microsoft for a token scoped to mail instead of sending a password.

• POP3 and IMAP4 are enabled per user by default, unless a tenant setting turns them off.
• An administrator can enable or disable IMAP4 for a single user, which is the smallest change that unblocks one mailbox.
• Microsoft notes that each POP or IMAP sign-in costs a few extra seconds because of an authentication proxy hop; a background sync absorbs that, and you will not feel it in the list.

Connect Microsoft 365 to Mailbind

1. 1Sign in to Mailbind and choose “Connect a mailbox”.
2. 2Type the address. Mailbind looks up the domain and names Microsoft 365 itself when the records say so; otherwise pick Microsoft 365 from the list.
3. 3Enter your name as you want it to appear on outgoing mail, then use “Continue with Microsoft” where your tenant allows it, or enter the mailbox password if basic authentication is still on.
4. 4Check the server settings. They are filled in from the preset, and you can edit either side if your account is on a different host.
5. 5Press “Test and connect”. Mailbind opens IMAP and SMTP before it saves anything, so a wrong password or a blocked port is a message on the form rather than a mailbox that silently never syncs.
6. 6Name the mailbox for the sidebar, pick a colour, and the first sync begins immediately.

Mailbind only connects to the four ports email uses — 993 and 143 for IMAP, 465 and 587 for SMTP — and refuses private or loopback addresses. If your provider asks for a different port, it cannot be used here.

Shared mailboxes and distribution lists

A Microsoft 365 shared mailbox has no password of its own, so it cannot be connected as an account in the ordinary way. The usual answer is to give it a licence and credentials, or to connect it through a user who has full access and treat it as a second address on that mailbox. Either way, Mailbind’s own shared inbox is what makes it a team queue once it is connected: assignment, internal notes and a reply that leaves from the shared address.

A distribution list or a Microsoft 365 group is not a mailbox and has nothing to connect to. If your team answers from one, the mail has to land in a real mailbox first.

If it does not connect

• “Invalid credentials” for every user on the tenant: basic authentication is disabled, or security defaults are on. Use OAuth.
• One user cannot connect while others can: IMAP4 is disabled for that mailbox.
• Receiving works and sending does not: check the outgoing host is smtp.office365.com and the port 587 with STARTTLS.
• Conditional access blocks the sign-in: your administrator needs to allow the client, which is a policy decision rather than a setting in Mailbind.

Common questions

Keep reading

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