Earlier this year, I had to email a colleague to ask them to send me some information I was waiting for. They insisted they'd sent it already but I couldn't find the email in Mail.app (both iOS and Mac) or Gmail.
The same thing happened today. A different colleague emailed me over the weekend. I saw the message arrive in my inbox on Saturday but didn't open it. This morning, I couldn't find it so I emailed the colleague asking them to send the info believing I might have imagined it the first time. The colleage replied. After reading the reply on my phone, I went to my mac, opened Mail and the message wasn't there! I couldn't find it on my phone or the Gmail web app either. I looked in junk and trash as well but still couldn't find it.
I've tried rebuilding the mailbox but the missing messgae is still missing.
It's a bit worrying as I do all my business over email. Why do my emails disappear sometimes? What can I do to prevent them from disappearing?
(From time to time, I hear the incoming mail alert but there's no new email in my inbox. Could that be related?)