Product and version (FileMaker Pro 16.0.4), Outlook 2016 latest version.
OS: Windows Server 2012 R2, terminal server using RDC connections.
60.5 GB RAM
240 GB NTFS hard drive
*Everything meets recommended / minimum requirements.
When using Send Mail [via Client] with Outlook 2016 "Unknown Error" occurs after 2-4 attempts. To clarify, the first few attempts open Outlook client properly and create a draft. After several uses however, the script step begins failing, returning Unknown Error (-1).
Note: Outlook 2016 and FileMaker appear to be working correctly on all work stations / servers besides the terminal server users.
Ensured win.ini file is correctly configured, rebooted machine.
Repaired Office 365 installation.
Completely re-installed Office 365 installation.
Completely re-installed FileMaker Pro 16.0.4.
Tested multiple accounts and multiple outlook accounts.
Tested script steps with and without attachments, with and without other parameters.
How to replicate
Send mail step on RDC deployment of FileMaker with latest version of Outlook client. Ensure outlook is configured with a live account--if no outlook account is downloaded, there will be no errors.
Workaround (if any)
Restarting FileMaker and Outlook applications resolves the issue for another 2-4 attempts.
At this point, I will be looking into third-party plugins to resolve the issue and resume business in a timely fashion.