Default post for SSH on Mac is 22 as far as I know.
Try:
ssh myusername@externalip:22
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Again, you're not in front of you mac so I am not sure if this would help. You would need to have that port forwarded to you Mac.
Try:
ssh myusername@externalip:22
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Again, you're not in front of you mac so I am not sure if this would help. You would need to have that port forwarded to you Mac.