Once, I almost didn't get a job because my email address got miscommunicated.
When I was first applying for "real" jobs after finishing undergrad, I didn't have my own domain name yet, and had put my <firstname><lastname>@<university>.edu email address on my (paper) résumé, which I then handed off to recruiters at the career fair. A few companies expressed interest in doing first-stage interviews with me, which were carried out on campus. I made those appointments, showed up, and eventually all of those companies' recruiters got back to me to let me know whether they wanted to proceed — all except one. I metaphorically shrugged, assumed they weren't interested, and carried on with the companies who'd invited me back for the next stage.
However, a couple of weeks later, in the middle of spring break, I was woken up by a call from the company that hadn't responded. "We just wanted to check whether you're still interested in continuing the application process with us," the recruiter asked me as I tried to conceal the fact that her early afternoon was my early morning. "We've sent you several emails, but we haven't heard anything back." That was odd. To the best of my knowledge, I hadn't received any emails from them at all. Maybe they had gotten marked as spam? I asked the recruiter which email address she had on file for me, so that I could be sure I was looking in the right place. "We have you down as <firstname>.<lastname>@<university>.edu," came the answer.
Did you catch the mistake? Read that last sentence again if you didn't. I'll wait.
Especially in a world where <firstname>.<lastname> is one of the most common formats for an email address, it's not all that odd that my underscore got replaced by a dot. I don't remember, if I ever knew, where the mistake happened — someone might have misread my résumé, I might have written my email address down on paper and made the underscore too short, etc. — but it would be beside the point even if I did. This is something that anyone could do by accident, even if transcribing emails is their job that they do all day, everyday. It's worth having a system in place to prevent it.
The lesson here is twofold. Firstly, double-checking is vital. This would probably never have happened if everyone involved in the process had taken just one more second to make sure they were typing the exact same sequence of characters that was on the piece of paper in front of them, or if applications had been filtered through a system that allowed for automated error checking or email verification. Secondly, though, it is important to always have multiple ways of contacting someone if you want to be sure that you remain in touch. Historically this has meant a phone number and an email, although in an ideal world in which we were already phasing phone numbers out entirely it would make more sense to ask for, say, email + LinkedIn on a job application and email + some other handle in non-professional contexts.