Domain name with Company A, Email with Company B and VPS with Company C... A Record or Nameservers to join things together?

I do some freelance web development and have spent a long time with a single host that provides all services (domain name, website/database hosting and email) under one account.

I am looking at improving my services but also keep costs down. My current provider has a package where I can register domain, email and a VPS but the cost is quite high. I have researched that I could spread the services to different providers, but I am unsure how this would work with DNS and existing records.

My domain name example.com is registered with Fasthosts (UK), my email is provided through Office 365 (with all the correct DNS records pointing from Fasthosts to Office 365) and I would like to run my own VPS through a different company again.

To add to this: I would also like to be able to host a number of customer websites through my VPS but also be able to provide email to them through Office 365 (I have a tenant account). They may want to keep their domain names with their own company, or I register them through Fasthosts.

Question number 1 (I guess): For my own domain (example.com) do I just need to create an A record to point my www traffic to my VPS IP? I think I've answered my own question as this seems fairly logical.

Question 2 (main question): For my customers who have their domain names hosted elsewhere but only want their website on my VPS, do I just need to, again, point an A record on their domain DNS to my VPS IP?

Do I need to do anything with nameservers, or is that if they want ALL services provided by my hosting company? So, in theory, the customer's domain registrar is just that - no services provided by them apart from the domain admin?

Answer

To answer your questions, yes, all you need to do is change the A record(s).

The easiest way is to get your clients to change the A record for www (or whatever hostname) on their DNS servers to your VPS IP. You do not need to move domains to your hosting provider's DNS servers.

Make sure the IP of your VPS is static as well. If not you will need dynamic DNS.