Integrating external email accounts
In the mailbox webmail client, you can link external email accounts from other providers such as GMX, web.de or mail.de.
Benefits of linking external accounts
Linking external accounts offers you a number of benefits:
- You can read emails from the linked accounts directly in the mailbox webmail client.
- You can send emails using the sender address of the integrated account directly from the mailbox webmail client.
- You can manage all your email accounts in one place via the mailbox webmail client.
- With the Unified Mail feature, you can even use shared folders across multiple email accounts, e.g. a central inbox or a shared folder for sent messages.
Settings for external providers
With some providers, it is necessary to configure specific settings for integration. The provider must allow access via IMAP or POP3, as well as SMTP (for sending emails).
Please consult your provider’s documentation or support team for further details.
Options for integrating an external inbox
mailbox as an email client for external inboxes
The mailbox webmail client can act as an email client and display messages from the external provider separately. You will then have an additional, separate inbox beneath your mailbox account. You can integrate both external and mailbox inboxes that are to be used by several people at the same time.
This section explains how to fully integrate an external email address: Fully integrate an external email address.
Retrieving emails from an external address via POP3
If you use the POP3 protocol to retrieve emails from your external provider, all emails are retrieved from there and then deleted – at least by default with the POP3 protocol. The messages are then only stored in your inbox.
The following article describes how to set up an external POP3 account with mailbox: POP3 support with mailbox.
Setting up an external email address as an alternative sender (Mail Relay)
With Mail Relay, you integrate an external inbox into the mailbox webmail client so that you can send emails using the external email address via the mailbox servers. The address of the external mailbox will be displayed for selection in the From field when you compose a new email.
It is not possible to receive emails from the external address in your mailbox inbox using this method.
The following article describes how to set up Mail Relay: Setting up an external email address as the sender in mailbox
Setting up a central inbox (Unified Mail)
With Unified Mail, you get a central overview of all your inboxes and sent messages without having to constantly switch between different accounts. When integrating multiple inboxes, the Sent Items and Inbox folders from all inboxes are combined. This keeps your mailbox organised.
The following article describes how to set up Unified Mail: Setting up a centralised inbox (Unified Mail)
Notes on integrating a Gmail account
Direct integration of Gmail accounts into the mailbox webmail client is currently not reliably possible. Google discontinued support for the previous method of logging in with a standard Google password for third-party applications in May 2025.
Instead, Google relies on modern authentication methods such as OAuth 2.0. This authentication method is not currently supported when integrating external email accounts into mailbox.
Under certain conditions, it is possible to connect using an app password generated by Google. However, as Google may still block access, long-term functionality cannot be guaranteed using this method.
Alternative: If you wish to manage your Gmail account alongside your mailbox account in an email programme, you can use a programme (e.g. Thunderbird) that supports logging in to Google via OAuth 2.0. The Gmail account is set up directly within the email programme and is not integrated into the mailbox webmail client.
Notes on integrating an Outlook.com account
Please note that Outlook.com accounts cannot currently be integrated into the mailbox webmail client as external email accounts.
The reason for this is that Microsoft requires the OAuth 2.0 (Modern Authentication) authentication method for accessing these accounts via IMAP and SMTP. This method is not currently supported by the feature for integrating external email accounts into mailbox.
This restriction applies exclusively to the integration of Microsoft accounts into the mailbox webmail client. You can still use your Outlook.com account with a standalone email programme, provided it supports OAuth 2.0.
