Job application etiquette

[Dressedilemma]

Just had an email from the HR department asking me to upload some documents to their recruiting platform to see if they want to call me for interview. The email isn't signed by anyone, just
"Thank you in advance.
Kind regards
hr@ company name"

I've uploaded the documents. Should I answer the email saying I've done it? or is the fact I've done it answer enough?

Additional complication, I'm currently abroad and although I bought extra data and have roaming turned on (in case they call) I can't be 100% sure they will get me if they call as last time I was abroad my doctor tried to get hold of me and couldn't.

I would email, as although they will check and email will put you in the queue - we use the same system.

I would also state I am currently abroad and will be available for a call at XY or Z time

Yes reply. Even if it's not needed it shows you've acknowledged the email and your character as an employee. Also ask them to email you rather than call due to your holiday / phone issues

How do you start an email when you don't know the recipient? Is it like a letter "Dear Sir/Madam"or is that outdated now?

I always think starting an email with "Hi' is fine, even in formal circumstances. Let's see if others disagree.

Thank you very much for your email, I have uploaded the requested documents. Please note that I am abroad until Saturday and might not be contactable by phone.
Kind regards
Me

Don't state you might not be contactable. Instead say you may have only intermittent access to emails and messages, but will try to respond as soon as possible.

Dear hiring manager,

I have completed and returned the forms via the electronic system. Please do let me know if you don’t receive them. I am currently abroad and unsure if the process will work correctly.

Best wishes,
Jane Davis

Staring an email with Hi is never acceptable unless you know the person.

Absolutely depends on the sector. Charity recruiting manager here and ‘hi’ is very much the norm.