godan verb (-su), transitive verb
send word; write to; inform (humble)
Humble verb (謙譲語) used when the speaker sends a message or writes to a superior or someone outside their group. Often used in formal letters or business contexts. The action is performed by the speaker or their in-group toward the recipient.
詳細が決まり次第、改めて申し越します。
I will send word again as soon as the details are decided.
先日はお手紙を申し越し、ありがとうございました。
Thank you for the letter you sent the other day. (humble perspective: the speaker is grateful for the recipient's action of sending, but the verb is used from the speaker's side in a formal acknowledgment)