Commonly advertises generally being an "open source email service" while it's specifically just their email clients which are open source. From their position of being an E2EE email service they might be thinking that all the value in regards to privacy and functionality is in the apps (which it may well be) but the wording can still mislead folks into thinking the whole service itself is open source.
Tuta is open source so security experts can verify the code that protects your emails. ref
For these reasons it was also crucial for us to publish the entire client code for Tuta under GPLv3 as free software. ref
Notification
A previous thread of this being raised can be found 5 years ago on Reddit here, where Tutanota indicated they would make improvements. They also note their intent to open source the server side also.
Here's an update on the server-side not being open from 10 months ago (not specific to open source wording).
Their content/site has probably change a lot since that 5 years post, so probably worth querying again.
Commonly advertises generally being an "open source email service" while it's specifically just their email clients which are open source. From their position of being an E2EE email service they might be thinking that all the value in regards to privacy and functionality is in the apps (which it may well be) but the wording can still mislead folks into thinking the whole service itself is open source.
Examples
Notification
A previous thread of this being raised can be found 5 years ago on Reddit here, where Tutanota indicated they would make improvements. They also note their intent to open source the server side also.
Here's an update on the server-side not being open from 10 months ago (not specific to open source wording).
Their content/site has probably change a lot since that 5 years post, so probably worth querying again.