Is it safe to send password over mail?

Recently I’ve been working as a contractor with a company, which requires me to often log in to different b2b services.

The way I receive the login data is usually over email in plain text. My gut feeling tells me sending sensitive data in plain text is not a good idea however I’m not sure if there is an alternative, or perhaps it protected by the mailing service (in this case gmail)?

I’m aware of probably the most obvious danger which would be leaving my account logged in and unattended, however I’m more interested in some kind of a man in the middle attacks or other dangers.