Email through Outlook Failing

Hello All,

I have an application (written in Windev 12) that has been working for a bout 9 months. It sends out pdf document via emails through MS Outlook. It has worked well until just a month ago.

Now some emails (about 30-40%) goes through but others are sent alright only to get a feedback "Undeliverable". A close examination of the returned mail shows;

IMCEAEX-_o=GLOBALTRAK_ou=Exchange+20Administrative+20Group+20+28FYDIBOHF23SPDLT+29_cn=Recipients_cn=e55fe3844cae469e9fce40dd8b13b86b-Mark+20Monroe@GLOBALTRAK500.COM Remote Server returned '550 5.1.1 RESOLVER.ADR.ExRecipNotFound; not found'

A close look at the returned email shows that the email address of the recipient is prefixed with the above error like this :

"IMCEAEX-_o=GLOBALTRAK_ou=Exchange+20Administrative+20Group+20+28FYDIBOHF23SPDLT+29_cn=Recipients_cn=e55fe3844cae469e9fce40dd8b13b86b-Mark+20Monroe@GLOBALTRAK500.COM"

The strange thing is some emails go through and some don't though all used to go through previously.

Any help would be appreciated. The command to open MS-Oulook session is

SessionID = OutlookStartSession("")
IF SessionID>0 THEN
Zcnt=SessionID
ELSE
Info("Could not locate MS Outlook installation or setup not compatible with this system...")
ReturnToCapture(COMBO_clktoreport)
END

Sam