Need an email recommendation

I've been using MailDroid Pro for a long long time with absolutely no problems on my GS 8+ until a couple of weeks ago at which point it's gone really bad...like milk left outside the fridge.

First, it will no longer open PDF attachments to emails (this is a damned disaster for me as all of the attachments to business emails are all PDFs.
when I click on the PDF attachment paper clip, an error message comes up that says "Error: [AUTHENTICATION..."

Of what??? Anyone know? Yes I have...

Need an email recommendation

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