I was sent on a business trip overseas for 3 weeks, with 5 people from 5 different departments. Because of some business complications, the timeline for what we needed to do there was super tight. While I understand that and understand that everyone works together and does a bit of everyone's work where we can help, last weekend, two of the guys (let's call them E and C) decided to do my job and over the weekend did what I was supposed to produce. They sent it out, saying they took the weekend to do this, when it was clearly my department's deliverable. I became very, very mad that they did such a thing because I feel they should have at least included me in the discussion since it was clearly my department's responsibility.
I sent an email to my manager (who for personal reasons couldn't make this trip) letting him know of my feelings regarding what had happened. I sort of "went off" - in the email, I stated that I am shocked that this happened and asked what his advice would be. I also met with C the next day and told him that it was insulting to me because it made me feel like I'm not doing what I'm supposed to do, or not pulling my weight.
After a few days of cooling off, I'm starting to think I shouldn't have sent out the email to my manager. What is your take? I still think what they did was disrespectful and insulting, both on a personal and professional level, for someone to go right out and do someone else's work without involving or at least letting them know about it.
I understand why you feel the way you do, but yeah, you didn't really handle this well -- largely because you jumped to the worst conclusion immediately.
Rather than immediately deciding to feel insulted and disrespected, why not start off by thinking, "Hmmm, we're clearly on different pages, so let's figure out why." Ideally, if you could re-do this, you would have thanked E and C for their help, but also nicely explained that you need to be in the loop when your department's work is being done -- because you might have already been in the midst of finishing it, or because you might have information they don't have that would impact things, or simply because that's what you're there to do. You would have then asked them, "Going forward, does that sound reasonable, or should we handle this stuff some other way?" And then you would have waited to hear their response with an open mind. Maybe they actually had good reason for what they did, and you might have changed your mind if you heard them out calmly and non-defensively. Or maybe they'd realize they had overstepped their bounds and would agree to work with you differently in the future. But this approach is the best way to get at that in a professional way.
The key to this way of thinking is that you're not just "mad because they did my work." You need to go beyond that to explain why that's a problem (even if the "why" seems obvious to you). That's how you turn an emotional reaction into a professional one. Otherwise, even though of course division of labor is important and there for a reason, your reaction can sound more like a turf war, that you're not a team player, etc. You might have completely legitimate reasons for being upset about this -- but you have to calmly articulate why this creates a problem, not just fall back on "this was mine to do."
(By the way, a disclaimer: I'm assuming that E and C really shouldn't have done what they did -- although it's possible that everyone was supposed to be pitching in on everything. Since I don't know, I'm assuming the former.)
Your email to your boss was a bad idea for the reasons above. I'd send a follow-up telling him that you overreacted and that you're going to take a more constructive approach with C and E. Keep it short, calm, and unemotional.
Last, this has to be said too: It's worth thinking about why C and E stepped in. Maybe they did your work for innocent reasons (eager to help, on a roll, unclear about division of labor, working on something related and this was natural to include, just not thinking, etc.) ... but maybe they did your work because they don't think you're going to do it well, or fast enough, or at all. This last possibility is the one that insulted you, of course -- but you should ask yourself honestly if there's any reason for them to think that. The fact that you were so emotional about it might indicate that there's some truth to it, simply because if you were 100% confident about your work, I don't think this would have felt as threatening to you. So be really, really truthful with yourself if there's anything like that going on ... and if there's not, great, but it's worth taking a look at.