Learn Hardcore Korean: sukso jusoreul mesijiro bonae juseyo. - Please send the accommodation address by message.

를 marks the direct object: 숙소 주소를 = “the accommodation address (as the thing being sent).”
In casual speech, Koreans often drop object markers if the meaning is clear. You might hear 숙소 주소 메시지로 보내 주세요, but with two noun phrases side by side it’s cleaner and more natural to keep 를, especially in writing.

What does 로 in 메시지로 mean? Could I say 메시지에?

-로/으로 marks “by/with/through” (means or method). 메시지로 = “via message.”
Do not use 에 here. 에(게) marks a location or recipient, not a means. If you want to name the recipient, add something like 저에게/저한테 before 메시지로.

Should I use 문자로, 메시지로, or 카톡으로? What’s the difference?

문자로: “by text (SMS).” Very common default in Korea for phone texts.
메시지로: generic “by message,” or specifically Apple’s Messages in some contexts. A bit broader/less specific than 문자.
카톡(으로): “via KakaoTalk,” the most common messenger in Korea.
Other channels: 이메일로 (by email), DM으로 (by DM), 왓츠앱으로 (by WhatsApp), etc. Use the one that matches the actual channel.

Why is it 보내 주세요 instead of just 보내요?

-아/어 주다 adds a benefactive/request nuance: “do X for me, please.”
보내요 is usually a statement (“[I/you] send”) and doesn’t sound like a polite request.
보내 주세요 is the standard polite way to ask someone to send something.

Is the spacing 보내 주세요 or 보내주세요?

Standard spacing writes auxiliary 주다 separately: 보내 주세요.
In everyday texting, 보내주세요 is extremely common and generally tolerated.
For formal writing (emails, reports, tests), prefer 보내 주세요.

Who is the subject and recipient here? How do I say “to me” explicitly?

Korean often drops obvious elements. Here, the understood subject is “you,” and the recipient is “me.”
To make it explicit: 숙소 주소를 저한테(=to me) 메시지로 보내 주세요.
- 저한테 (casual/spoken), 저에게 (more formal), 선생님께 (honorific recipient).

Can I say 숙소의 주소 instead of 숙소 주소?

Both are correct. In everyday speech, noun–noun compounds without 의 are more natural: 숙소 주소.
숙소의 주소 sounds more formal or written, or used when you need extra clarity or emphasis on possession.

Can I change the word order?

Yes. Korean is flexible with adverbials like 메시지로.

메시지로 숙소 주소를 보내 주세요.
숙소 주소를 보내 주세요. 메시지로요. Word order mainly affects emphasis; meaning stays the same.

How polite is -주세요? What are softer or more formal alternatives?

Rough guide from casual to very formal:

보내 줘 (intimate)
보내 줘요 (polite casual)
보내 주세요 (polite neutral; your sentence)
보내 주시겠어요? / 보내 주실 수 있을까요? (softer/more deferential)
보내 주시면 감사하겠습니다. (very polite, typical in emails)
보내 주십시오. (formal/official imperative) Also possible: 보내세요 (polite but more direct than using 주다).

Is 메세지 ever correct?

No. The correct spelling is 메시지. Writing 메세지 is a common mistake.

Any pronunciation tips for this sentence?

숙소 often sounds like “suk-sso” (the ㅅ is tensed).
문자 (if used) sounds like “mun-jja.”
메시지 is “me-si-ji” (not “me-se-ji”).
주세요 is “ju-se-yo.” Full phrase approximation: “suk-sso ju-so-reul me-si-ji-ro bo-nae ju-se-yo.”

Could I just say 보내세요 instead of 보내 주세요?

You can, but 보내세요 is more of a direct instruction. 보내 주세요 feels kinder and more cooperative.
If you want extra softness, use 보내 주시겠어요? or 보내 주실 수 있을까요?

What does adding 좀 do, as in 좀 보내 주세요?

좀 softens and makes the request sound more natural: 숙소 주소를 메시지로 좀 보내 주세요.
Avoid 제발 in normal requests; it can sound desperate or frustrated.

Can I use the topic marker: 숙소 주소는 메시지로 보내 주세요?

Yes. …는 topicalizes/contrasts: “As for the accommodation address, send it via message (as opposed to some other method).” Useful when contrasting with something else, e.g., 사진은 이메일로 보내 주세요.

When would I use 보내 드리다?

드리다 is the humble form of 주다, used when the speaker gives/does something for a higher-status person.
Use it when you are the sender: (제가) 주소를 메시지로 보내 드릴게요 (“I’ll send you the address by message”). Don’t use 드리다 when asking them to send something to you.