JonathanB.28139 (Robbins Geller Rudman Dowd, LLP) asked a question.
Mimecast - My Apps
With the GA of "My Apps" the current Mimecast Admin app causes admins who do an SP initiated flow; whether it was intended for the Admin portal or Personal Portal, to land on the Admin portal.
https://community.mimecast.com/community/service-updates/blog/2019/08/12/my-apps-is-available-to-all
Eg. Users browse to https://login.mimecast.com/apps with the intent of launching the Personal Portal -> User enters their E-mail address -> Mimecast kicks off an SP Initiated flow as their E-mail address triggers a matching authn profile -> User lands on Admin homepage. User can now manually browse to https://login.mimecast.com/apps
Thank you for posting on our Community page.
By the look of it, this issue seems to be on the Mimecast side. This is mainly because Okta does not handle deep links (e.g. https://login.mimecast.com/apps); the only thing that Okta does is to be sure the user is authorized to access the resource and redirect him back to the app; the redirection to the original link is always managed by the SP.
The best thing I can suggest would be to open a support case with them.
Thank you,
Cosmin Prahoveanu
Technical support engineer | Okta