Is it Islamically sufficient to appoint the fiancée's father to the Imam of the mosque in the groom's town of residence to conduct the marriage for his daughter, merely by sending a paper stating the authorization for marriage?

The father's authorization of the mosque's Imam to officiate his daughter's marriage contract is valid. The lack of a personal acquaintance between the father (guardian) and the agent (Imam) does not invalidate the authorization, as long as the agent is designated and qualified to officiate the marriage. These qualifications are: being male, an adult, free, Muslim, and of sound judgment.