Matching a key with other emails

[Parabola]

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Hi,

Some people in my keyring send and receive emails using multiple
addresses (say, name at isp.com and name at hotmail.com) but each one of them
just keep one keep key which only maps to one of the addresses (say,
name at isp.com). Now every time I'm sending / replying mails to their
secondary addresses (name at hotmail.com), my mail client (Mozilla +
Enigmail) will complain that it doesn't know name at hotmail.com and I have
to manually select the key that maps to name at isp.com.

Assume that I can't get them to add them secondary address to their
keys, is it possible for me to tell my GPG that "hey! mails sending to
name at hotmail.com should be using key that name at isp.com key!)?

Regards,
Parabola
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