Hi,
From your description above, one internal Lync user call another internal Lync user who set call forwarding to his mobile successfully. However, the caller who is external the domain will fail the
call.
If it is the case, please double check the 50,000-59,999 ports open inbound and outbound for Edge Server external A\V Service.
Please also verify Edge Server internal interface could route to Mediation Server.
Besides, please check PSTN provider settings as Linus mentioned cuz some PSTN providers will deny certain number outbound from your company due to some restricted configuration.
Kind regards,
Calvin Liu
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