SYMPTOMS

This article provides troubleshooting information for sending to large email providers such as Hotmail, Outlook.com, Yahoo and Gmail that may temporarily delay or reject your inbound message. These providers may also mark your email as junk or indicate that the sender is not authenticated. For example, Gmail may display a question mark for the senders avatar.

CAUSE

The most common reason for mail not being accepted by servers such as Hotmail, Yahoo, Gmail, AOL, etc. is due to a temporary delay or rejection. The causes for these are varied but normally a bounce message will be generated indicating that the sent message was either delayed or could not be delivered along with an SMTP error code that the remote server generated during the SMTP transaction. The error code that is returned in the bounce should also be logged within the MailEnable SMTP log files. Usually the large email providers will also provide a URL that can assist in troubleshooting the SMTP error and provide detailed information relating to the delay/rejection.

RESOLUTION

Here are some troubleshooting guides from the various providers that contain detailed bounce errors and links to articles to address each of them:

Gmail: https://support.google.com/a/answer/3726730?hl=en

Outlook.com: https://mail.live.com/mail/troubleshooting.aspx

AOL/Yahoo: https://postmaster.verizonmedia.com

Below are some best practices that need to be implemented within MailEnable to prevent delays and rejections from remote mail servers:

• Test to see if the MailEnable server is not open relay: https://www.mailenable.com/kb/content/article.asp?ID=ME020168
• Test if the server has been spammed through, see this link: https://www.mailenable.com/kb/content/article.asp?ID=ME020339
• Ensure a PTR record (Reverse DNS record) has been set. Most servers, especially large ISPs will complete a Reverse Lookup on your IP for verification purposes.  One way this is done is via a reverse lookup to the PTR record of the IP address. This looks up the IP address to see if there is a matching DNS entry. To confirm whether this is set up correctly, perform a Reverse Lookup on the IP address using the tool at https://mxtoolbox.com/blacklists.aspx or by checking in the MailEnable SMTP logs, the activity and debug will show errors and often supply resolution links for the large ISPs. If unsure as to how to add a reverse entry for your IP address, contact your hosting or service provider for help
• Test if the MailEnable servers outgoing IP address is not present on a spam blacklist: https://mxtoolbox.com/blacklists.aspx. For more information on removing the servers IP from blacklists please see: https://www.mailenable.com/kb/content/article.asp?ID=ME020166
• Configure the SMTP service to send using TLS. This is enabled in the administration program under the SMTP Outbound settings.
• Configure SPF records for your server. More details can be found at https://en.wikipedia.org/wiki/Sender_Policy_Framework. You don't need to make a change in the mail server settings to configure SPF for your domains, you do this by creating DNS entries.
• Configure DKIM for your local domains: https://www.mailenable.com/documentation/10.0/Enterprise/Domain_-_DKIM_(DomainKeys).html
• Do not configure catch-all accounts to redirect, as you could redirect spam and get your IP blacklisted.
• Do not redirect spam messages. Please review the following article on how to stop incoming spam before it can be redirected: https://www.mailenable.com/kb/content/article.asp?ID=ME020008
• Check your SMTP logs for any unsual emails being sent, or mails being sent to lists.
• If this is a new IP address it may not have any reputation as a mail server and could be blocked.
• If you are being blocked by Outlook.com be sure to sign up at https://sendersupport.olc.protection.outlook.com/pm/services.aspx to get feedback on your deliveries.
• You can request to be removed from Outlook.com blacklist at https://support.microsoft.com/en-us/supportrequestform/8ad563e3-288e-2a61-8122-3ba03d6b8d75 but make sure you are not sending spam to them before doing so.