Apple Mail crashing on iPhone and iPad in iOS 11.2.6

Hi there, sebastian@gos!
Thanks for reaching out to the Apple Support Communities! It sounds like you are having an issue with you mail app crashing due to a strange file in an email and I am happy to help out! I recommend logging into the webmail for your account on the internet and deleting the email, then check out this article with steps for How to force an app to close on your iPhone, iPad, or iPod touch and close the Mail app. Once that is done, Restart your iPhone, iPad, or iPod touch and see if the Mail app is opening properly.
Take care!

Hi i have same Problems with smime, in i will Write any E-Mail to sime Secure Adresse Mail App Crashs all Time (11.2.6)