MX Records and A Records Updated But Email Addresses Can Still Send Email [closed]

I have updated the MX Records, the A records, the Z records and the cname for a particular domain but the emails registered with the hosting provider can still send email. The changes have definitely propagated since the mail boxes can no longer receive email.

Why can these email addresses still send outgoing email? The test messages I've sent to my google account say "encryption: name_of_hosting_provider.com did not encrypt this message".

I need these email addresses disabled, unable to send or receive email.

I'm going to adress your question and some of your comments in this answer. You have a misunderstanding of how email works and how hosting providers work.

I have updated the MX Records, the A records, the Z records and the cname for a particular domain but the emails registered with the hosting provider can still send email

Of course they can. The MX and A records have nothing to do with what user accounts and email addresses I can set up on my email server. I can set up an email server for microsoft.com and create a user account and email address for [email protected] and use that to send email to my hearts content. Whether or not a receiving server accepts these emails is entirely up to them. If they check for and use SPF, DKIM and DMARC then chances are my email will be rejected. That doesn't negate the fact that I can set this up if I so choose. There's no universal database or authority that says "Hey, you can't set up an email server for Microsoft and send email from [email protected]!". Of course, I can't receive any email to my [email protected] email address... because I'm not really Bill Gates and I don't control the MX record for the microsoft.com domain and therefore can't designate my email server as the MX record for the microsoft.com domain. The MX record doesn't prevent me from setting up my email server for the microsoft.com domain, it only prevents me from receiving email for the microsoft.com domain (and in most cases will prevent my email from [email protected] from being accepted. It doesn't prevent me from sending it, but most email servers will reject it upon receiving it).

Since I was going to get new hosting for the domain anyway, I thought changing the MX records would disable the email addresses that were registered with the old hosting provider (because their MX records will be obsolete) but that did not happen

MX records have nothing to do with user accounts or mailboxes. MX records designate which host(s) receive email for a given domain. They're not used to validate user accounts or email addresses. Changing the MX record means that the old email server will no longer receive email for that domain but it doesn't mean that those user accounts and mailboxes are now magically disabled. They are completely internal to the hosting provider and unrelated to DNS. Email from those user accounts and email addresses can still be sent. It's up to the receiving server to decide whether to accept them or not (based on SPF, DKIM and DMARC).

One would have thought that the receiving server would check if the MX Record matched the address of the originating server or not. Apparently they don't

They're completely independent accounts hosted at two entirely different providers. The fact that they share the same usernames and email addresses is meaningless. Furthermore, MX records designate which host(s) receive email for a given domain while SPF records designate which host(s) send email for a given domain. These hosts are not always and not necessarily the same. So what if I had one host that receives email for my domain and another host that sends email for my domain? Imagine what would happen if your email server checked the MX record for my domain when I sent you an email and your server said "Hey, this server sending me email from [email protected] isn't the same server that receives email for [email protected], I'm going to reject this email!"? My configuration is perfectly valid (an quite common) but your server rejects my email under the false pretense that the server that receives email for a domain (MX) should be the same server that sends email for a domain (SPF).