_My question needs some context:_

I have been hired by a small medical firm to, most importantly, establish and maintain secure communications between about 20 employees and clients. The contract also covers various other tasks such as teaching employees how to use Excel effectively and maintaining a website.

I've had many jobs before, but never had I been in charge of a project or were the most knowledgeable person in the subject matter. I am in direct communication with the business owners as well as the top manager. I advised them on the different choices we had and the owners, upon my recommendation, chose to use FOSS.

Once the owners took the decision, I informed the team of the changes that would be taking place, making sure to be as clear as possible and naming every piece of software that would be used. The top manager took the initiative of performing installation on some workstations before I began my work.

I have just last week completed the installation and configuration of gpg4win, Enigmail and Thunderbird for the selected users. Migration was a breeze, and user adoption is going very well. There have been no problems reported to me in a week (let's hope it'll last).

Now that everything has been set up, the head manager has suggested to the owners that we could instead use the gpg4win Outlook plugin to carry out the encryption so as to benefit from Microsoft's support if needed.

Ignoring technical details concerning the pros/cons of his proposition, what I'm asking is how do I deal with such behaviour? I am not in bad terms with the manager at all, but I do think he should not interfere or influence my job. This might be where I am mistaken.

Is such behaviour normal and desired, or am I right in thinking that division of labour (and hence my work) should be respected? If yes, then how would I deal with this?