Дмитрий Стародубцев
Правильный вариант:
Get-DynamicDistributionGroup "testgrp" | Set-DynamicDistributionGroup -RecipientFilter {(RecipientType -eq 'UserMailbox') -and (RecipientType -eq 'MailUser') -and (-not(CustomAttribute1 -eq "EXT"))}
Поправка. Вот правильный:
Get-DynamicDistributionGroup "testgrp" | Set-DynamicDistributionGroup -RecipientFilter {((RecipientType -eq 'UserMailbox') -or (RecipientType -eq 'MailUser')) -and (-not(CustomAttribute1 -like "EXT"))}