"My friends sent me a postcard."
Translation:Οι φίλοι μου μου έστειλαν μία ταχυδρομική κάρτα.
No, it isn't. The first is the possessive my and the second is me: "My friends" = οι φίλοι μου, "μου έστειλαν" = sent me.
What are the rules for accenting the second μου, as in one of the correct answers I had to choose in multiple choice?
As far as I know:
No accent on the second μου, since it's not ambiguous -- it's clear that it must be "to me" rather than "my".
If that is the case, there is a wrong answer in the database that must be selected in multiple choice. (On strengthen skills.)
I've moved the version with μού from the "best" version to a plain alternative; hopefully, this will stop it from appearing as a mandatory option in multiple-choice questions.
(On mobile versions, you may need to wait for an app update.)
mizinamo I think the second "μου" requires an accent, but it is DL that cannot support it. I don't think that it's a matter of ambiguity; it's a rule that Ι cannot cite. For example: μού έδωσε versus δώσε μου.