Motivated by a curious case on which a certain priest prohibited the faithful to share the e-mails he sends about mass times on message groups, I began to wonder what are the limits to priestly authority.

I mean, the faithful are required to obey the priests about spiritual matters only. At least that's my understanding.

For instance, can a priest order you to quit your job (presuming it is not an immoral work)? Can a priest prohibit you from wearing red shoes? Can a priest give orders to a Catholic monarch about state affairs?

I could not find any good resources about this.

If he is your diocesan priest, he has more authority over you than an sspx, fssp, independent, etc.

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What you call a "diocesan priest" doesn't have the authority to command a dog to roll over. He is a heretic posing as a Catholic priest.

  He may skip over a person who presents for Communion while wearing certainly immodest or inappropriate clothing. 

He may ban a person from Mass or from entering the church or premises in extreme situations, usually involving the civil authorities, but also if disturbing the Faith or well-being of others. 

If a priest (or anyone worthy of respect) requests not to share emails, you should respect the request.  It’s not a matter of ecclesiastical authority.  A priest may not abuse ecclesiastical authority by demanding information or actions not pertaining to faith or morals.  Example, a priest may withhold absolution if a penitent lacks contrition or shows no effort in eliminating a persistent mortal sin.  He may skip over a person who presents for Communion while wearing certainly immodest or inappropriate clothing.  He may ban a person from Mass or from entering the church or premises in extreme situations, usually involving the civil authorities, but also if disturbing the Faith or well-being of others. 
A priest may not impose ecclesiastical restrictions in personal or private matters.  Example, the case of an elderly woman banned from the Sacraments because she included the priest’s rival in a group of people invited for tea.  He told her she must confess this as a mortal sin before being readmitted to receiving Our Lord.  A priest may not impose unreasonable penances because of his personal dislike of a parishioner.  A priest may not inquire into parishioners’ private lives without a reason to do with the salvation of his soul.  He may not demand to know someone’s income, the worth of his home or other possessions, command that he cut off friendship with a non-Catholic for the sole reason that he is not Catholic.  A priest may not gain private information about others by asking his family or friends. 
It’s really not complicated.  A priest should confine himself to the duties of the priesthood, the salvation of the souls under his care.  In turn, a parishioner should show the priest like respect. 

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9. Women and girls who wear immodest clothes are to be prohibited from Holy Communion and from the office of sponsor in the sacraments of Baptism and Confirmation, and in certain cases, they are to be prohibited even from entry into the church.
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" for attending mass of a sedevecanti priest when he came to town once a month"