Sadly, email is not an entirely reliable communications medium, thanks to spam filters, addressing errors, and server failures. With certain types of email, it’s worth double-checking that a message was seen. One example of that I see is with reports of phishing email, which miscreants use to try to trick you into revealing passwords, credit card info, or other sensitive information. Phishing messages can be tricky to identify—that’s their goal. If you’re forwarding a possible phishing email to me or to someone else such as the supposed sender for evaluation, remember that spam filters often catch such messages because you are including content that might be spam, so your question may go unseen. To work around this, send a separate message or call saying you’ve forwarded what you think might be a phishing message so the recipient knows to check their Junk mailbox if need be.