The number one concern of substantially every company with more than 10 engineers right now is hiring additional engineers. You can't make a hiring manager who is looking for an engineer mad by offering to introduce him to an engineer.
I'd take time to customize the pitch and make it obvious that you're sending it to someone who may be or may know a good fit, as opposed to any routable inbox you can find from the Internet.
example one:
Dear sir,
I am a C# Java C++ engineer from $LOCATION with extensive experience in mobile applications, front-ends, ... <-- absolutely nothing in here suggests that they know who I am, and they're imposing on me because they're offering nothing of value to me.
example two:
Hey Patrick!
I've read between the lines of some of your recent posts, and it seems like you are overwhelmed on Appointment Reminder. [Patrick notes: Someone literally wrote this to me last week. Got my attention in a hurry.] I'm an experienced Rails engineer with 6 years of experience working with legacy codebases. I think I could take the engineering work for AR off of your plate, so that you can focus on marketing/sales. Would you like to have a chat about what that could look like? I am open on next Monday and Tuesday from $TIME to $TIME -- what half-hour in there works best for you?
<-- Even if I were not interested in this, I'd be interested in this. It is very respectful of my time, demonstrates unique understanding of my situation, etc.
