[exim] Fallback local delivery

Hi

Can you please help me to implement following behaivour:
1. When a message is sent to rcpt@??? it is accept by custom_router.
It is possible that MX server at domain.com some time is not available.

custom_router:
driver = dnslookup
transport = remote_smtp
domains = domain.com

2. While recipient's MX is down message is still in queue and tried to be
delivered by custom retry rule (queue runner is also 20 min):
domain.com * F,12h,20m;

3. Here is the my question.
When a retry timeout exceeded i do not want to sent a bounce to the sender.
I need to save that message (any method of local delivery.)

Please suggest me which option i can use, if it is applicable here.

Thank you.
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