Security certificate issue with Spark mail client

Since a few updates I’m unable to get spark running on iOS. I have an exchange mail box. Mailing the spark helpdesk did not result in any reply…
I get an error message that the security for the server is invalid or expired. If I try to continue an error pops up saying ‘unable to authenticate with the current sessions credentials’.
What is going wrong and how to solve this issue?
I’m running the latest version of IOS as well as Spark.

Is it possible that the security certificate on the Exchange server has expired? This happened on our test server recently and several people noted issues across mail clients when it happened.

Can be, I will have my provider look at that. Although other mail clients don’t report this issue.

Enter your domain for your Exchange server into the checker in the “Internet Email Security May Be Easier Than You Think” section on this page:

It should tell you is there is a certificate issue.

I’m wondering if Spark is perhaps the only client you have tried that is actually checking the certificate?