Indirect Objects in Passive Sentences (Is に Ambiguous)

Question

For verbs that typically use に in the dative sense (indirect object) like 送る (for example 手紙を先生に送った), is there any ambiguity in the function of に when the verb is used in the passive? For example, take the following sentences?

1. 手紙が先生に送られた。

2. 手紙を先生に送られた。

Can sentence 1 mean either "The letter was sent by the teacher" or "The letter was sent to the teacher"? Is one more likely based on how it was said (maybe a native would have intentionally used によって or something to clarify)?

Can sentence 2 mean "I was unfortunately sent a letter by my teacher" or "A letter was sent to the teacher and it indirectly impacted me"?

Answer 1

「手紙が先生に送られた。」

Can sentence 1 mean either "The letter was sent by the teacher" or "The letter was sent to the teacher"?

It can only mean "The letter was sent to the teacher". To express "The letter was sent by the teacher", a direct translation would be 「手紙が先生によって送られた。」, but this is extremely awkward; it is way more natural to say 「手紙が先生から送られてきた。」

「手紙を先生に送られた。」

Can sentence 2 mean "I was unfortunately sent a letter by my teacher" or "A letter was sent to the teacher and it indirectly impacted me"?

It can only mean "I was unfortunately sent a letter by my teacher". To express "A letter was sent to the teacher and it indirectly impacted me", it would be 「先生に手紙が送られ(てしまっ)た」。