Send out is for mail or an object in the mail, you send off a person on vacation or as a farewell.

These are kind of tricky especially for a native Russian speaker, but practice makes perfect, wouldn’t you say? Send off: 1) Отправить запрос на. I’ve sent off for some books for my course. You can also say send away (to someone for something). 2) Быть удаленным с поля (British English). Ronaldo was sent off for a foul in the second half. 3) Отправить что-то куда-либо по почте (обычной или электронной). I’m sending the files off to my colleagues tomorrow. Send out: 1) Разослать. Have the invitations been sent out yet? 2) Излучать - синоним to emit. The sun sends out light and heat. I hope this helps.

Good question ! These phrasal verbs are highly colloquial and depend on context for meaning but perhaps the following sentences will help illustrate some of their most common forms of use. Native speakers know how to use them instinctively but foreign speakers would have to learn them context-by-context or as separate colloquialisms. I cannot think of any easy grammatical rules to follow in this respect although they probably exist. “Send out” - They have been missing for hours now. We will have to send out a search party “Send off” - He’s retiring from work tomorrow. We will have to give him a good send off “Send over” - Dad ! It’s expensive at Uni. When can you send over some more money. I’m broke. “Send in” - Diplomacy has not worked. We will have to send in the army