Do take care!
I had a situation several months back where an organisation bought in their local IT consultants and moved their mail system to Exchange/ Outlook 365, basically web based mail using Outlook. This in itself is not unusual, it has happened several times before and Outlook running in the cloud offers several benefits in terms of assisting people to work together, things like improved communications, shared calendar etc.
To get another mail server on line you need to change some of the settings in the hosting. I normally handle that, but in this case I passed the control panel user name and password to the consultant under the direction of the client.
Everything appeared to go smoothly, their mail came on line and we forgot about it and moved on. But……
Some months later the client tested and found out that mail was no longer being sent from the website to the email system. This had worked when it was set up but was not working now. I was called in at this point.
It turns out that the IT consultant had made some changes but not all of the changes. The hosting was still configured to be a local mail server, but the records for the mail server pointed off of the hosting. So there was a conflict. The conflict did not affect anything else, just mail from the website.
The IT consultant had also used new name servers, but failed to update the settings in the web site hosting as well.
The moral of this tale is make sure you understand what your IT consultant is doing, and after he has done it check that EVERYTHING still works, not just your local mail, but anything feeding into it. There is a close relationship with your website, the contact us form and your email.
This was the only time I never supervised the changes in my hosting, and the first time someone else broke something. I assumed they knew what they were doing.