This is the 14388th most frequent Russian word.
отправленными
"Sent" (plural instrumental form).
The word 'отправленными' is used as an instrumentive case of the adjective derived from the verb, describing the documents as having been sent.
Со всеми отправленными документами мы работаем ежедневно.
We work daily with all the sent documents.
Here, 'отправленными' functions to describe 'messages' in the instrumental case, indicating their state as having been sent.
Всё это было сказано в связи с отправленными сообщениями.
All of this was said in connection to the sent messages.
In this case, 'отправленными' modifies 'proposals' in the instrumental case, explaining their state of being sent.