Especially if they're asking for personal information such as banking pins, account numbers or email addresses. Often these emails will link through to bogus banking sites designed to fool you into providing all your personal details to criminals - a scam called
phishing. They will also use scare tactics to alarm you into responding, such as warning your account will be shut down. If in doubt, do not click on the link in the email. Go straight to your bank's website or simply make a phonecall to ascertain the email's validity.