- Verify your internet connection is working.
- Check that you are using the right email server settings.
- Confirm your password is working. Remember, passwords are case sensitive. If your password is not working, just reset it.
- Confirm you do not have a security conflict caused by your firewall or antivirus software. To see if this is often the issue, temporarily disable your security software, but remember to put it back on when you are done testing. Try sending/receiving your email. If you are all good to send/receive now, then you have to regulate or update your security software.
- Check Your SMTP Server Connection, which is tricky because even if your SMTP details are correct, the server itself can be down or not functioning for some reason.
- Change Your SMTP Port, outgoing mail server uses normally port 25, but some ISPs may block it because of the increasing spam traffic that has been passing through it. You can use then port 587 or 465.
- Good email service providers have sophisticated SPAM filters that detect which emails are legitimate and which are not. However, they are not always 100% reliable and sometimes legitimate emails can get caught in the net. To avoid this, you must check if any emails from people you recognize have gotten moved to your SPAM folder and, if so, mark them as safe.
- Emails that contain attachments can sometimes be blocked too. Although common file types such as Word docs, PDFs and Excel spreadsheets usually get through; even they can sometimes cause problems. When Word/Excel documents contain macros that are blocked but this is often common reason as there is a real danger of malware being smuggled in through the macros. In the case of enormous attachments, it is highly recommended that you simply use a secure file transfer application instead of zipping them. This is because ZIP files are often wont to deliver and unpack malware like CryptoLocker and CryptoWall.
- If your company uses group addresses such as sales@ or support@ then it is possible the email could have been sent there, rather than to your personal inbox. Check who else is in this group as they will have received it
- You should check that you do not have any Outlook rules set that might be moving or blocking the email or quarantining it. Check your Junk and Clutter folders to check if certain emails are being moved there. If they are, it will often be because they contain SPAM words or attachments that Outlook does not trust or because Clutter is attempting to ‘de-clutter’ your Inbox by ‘learning’ what you do and don’t want. You can even ask the sender to send just a blank email to check if it arrives successfully.
Apart from this check if there is any maintenance going on with Exchange be it O365 or Exchange On Prem.
Check if User account is locked.
Check if User account is expired.
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