Seems to happen at random for some users with the following error:-
There's a problem with the recipient's mailbox. Please try resending the message. If the problem continues, please contact your helpdesk.
The following organization rejected your message: SVRSHIR614.gloscc.gov.uk.
Diagnostic information for administrators:
Generating server: xxx
user1@abc.co.uk xxx Remote Server returned '554 5.2.0 STOREDRV.Deliver.Exception:StoragePermanentException.MapiExceptionMaxObjsExceeded;
Failed to process message due to a permanent exception with message Cannot set search criteria in SearchFolder. Try using fewer keywords at the same time, reducing the number of users in the From, To, Cc, and Bcc fields, and reducing the number of mailboxes
that are searched at the same time. 16.55847:99000000, 17.43559:00000000F0000000000000003E00000000000000, 20.52176:000F84840600000000000000, 20.50032:000F84847617000000000000, 255.23226:000F8484, 255.27962:30000000, 255.17082:E7040000, 0.27745:80030400, 4.21921:E7040000,
255.27962:FA000000, 255.1494:80030400, 1.40476:64000000, 1.56860:64000000, 4.65308:E7040000, 1.63016:30000000, 4.39640:E7040000, 5.10786:0000000031352E30302E313135362E3030303A5356525348495236313400000000000000, 255.1750:00000000, 0.26849:05060480, 255.21817:E7040000,
0.30353:05060480, 4.19089:E7040000, 0.18065:04060480, 4.26257:E7040000 [Stage: OnPromotedEvent][Agent: Conversations Processing Agent]'