"Replied to" is the past tense, and would technically require an object after the "to", showing what was replied to. E.g.:
"I replied to all PMs"
"Have been replied to" is the present perfect tense. Since it is a passive construction, the object comes before the verb phrase. E.g.:
"All PMs have been replied to"
This is technically incorrect, since the sentence ends with a preposition ("to"). However, "replied to" could be considered a verb in itself, ridding "to" of the property of preposition and rendering the sentence valid.
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moto