I've recently upgraded my VPS to a 4cores, 8gb ram and 180gb ssd. This VPS comes with 500 free email accounts with 2gb each. This weekend I will migrate from the old VPS to this new VPS everything, so I will recreate all email accounts, etc, and I am now questioning myself if should I still using the free email accounts or use the VPS as mail server too, the only reason why I would like to have my own mail server is because I would like to authenticate my emails with DKIM and SPF, as some of them are currently going to Spam I believe this will improve the delivery rate. So my question is, is it possible to authenticate those free accounts DKIM and SPF if I have access to the DNS of my domain, please note I have no control at all of those emails, the only control I have is that I can create and delete accounts, but I mean I don't console access or anything to mail server. For your context, the VPS is with 1and1 and the free accounts too.
Please note I have no experience with Mail Servers and DNS, I am php developer.
It seems you cannot do DKIM now (or it would be hard for you), so it's best to avoid SPF too.
If you want SPF entries in DNS, I would strongly recommend to also have DMARC entries and DKIM entries.
Here's why: many people on the Internet use forwarded addresses. They set up [email protected] but they auto-forward it to [email protected]. If you have only SPF, outoging mail from your server effectively cannot reach them. If you had DKIM, the mail would pass.
DMARC is a policy mechanism to accept messages that fail SPF if they succeed DKIM plus a check if the sender address is not mismatched plus checks related to subdomains of your domain. Loosely speaking.
DKIM is the hardest part of this entire setup. For outgoing email, it requires you to insert headers into emails. Since it seems 1and1 cannot do this (yet), so you need to set up your own exim/sendmail. Without going too much into details, I guess it could be too much of a steep learning curve if you are not trying to become a proficient email admin.