Slow outbound email processing when own SMTP server is usedIssue Administrators may get frequent SMTP Sender alerts or encounter slow email performance when using their own SMTP server and end up with a large queue of sys_email records waiting to be sent. If you are using your own mail server for sending emails as defined in Configure an email account, one or more of the following may occur: delays when the instance produces many notifications, receiving automated SMTP Sender alerts from ServiceNow Support because SMTP Sender jobs may be taking longer than 30 minutes to complete, or errors such as "you've reached your 24 hour limit for message recipients" after some number of emails.CauseCompared to the default ServiceNow SMTP account provided with your instance, any external SMTP Server you might use will have disadvantages. There is a network latency since ServiceNow mail servers are physically much closer to the host your instance is located on. Our SMTP servers are also designed for quickly sending emails out while your servers might need to run additional checks for domains, relay permissions, etc and these will decrease the rate of emails being sent. There are two main causes for email delays when using external SMTP servers: 1) Your SMTP server may be unable to handle the number of emails being generated by your instance. If your instance is generating 100 emails per minute during peak hours, your email server needs to be able to accept 100 emails per minute. 2) You may have misconfigured groups that add a large number of recipients to each email. Due to the nature of SMTP, recipients are added one by one to an email while sending. If your instance is trying to send an email with 100 recipients, and if it takes 100 ms to send an individual command to your SMTP server, it will take 100 x 100 = 1000 seconds just to add the recipients one by one which is approximately 1.5 minutes.If your email server has latency or performance issues and it takes 1 second to send a command to your SMTP server, that single email will take 15 minutes. Since emails are sent sequentially, any other email in the queue will be delayed by this amount of time as well. ResolutionFor #1, you will need to discuss the rate of emails that can be processed by your email server with your email server administrator. If additional logs are needed, please check the "Enable debug output" option in the sys_email_account record. This will output all the communication between the instance and the mail server in to the node logs. Please follow How to download localhost logs from all or selected nodes to download the node logs. The relevant lines will contain DEBUG: SMTP or DEBUG: IMAP such as 2022-09-20 00:20:37 (002) worker.3 worker.3 txid=3359b621874e DEBUG: SMTP: enable SASL2022-09-20 00:29:27 (018) worker.6 worker.6 txid=c96bfae9878e DEBUG: IMAP: AUTH: PLAIN and include all the SMTP commands sent by the instance and by the email server including the milisecond timestampes. Please share this information with your email administrator as it may help them identify where the email server is not responding as fast as expected. Do not forget to turn debugging off after troubleshooting, especially in production instances, as these options output all email traffic, including email content, to be output in to the node logs. This may cause node logs to be truncated after several gigabytes, and the node logs will become useless for troubleshooting other issues. #2 has a more visible effect when your first level assignment groups cause this issue, since first level assignment groups usually get many notifications when records are assigned to them. Please check the following: Check if your groups have a group email set and that Include Members is not selected unless necessary: /sys_user_group_list.do?sysparm_query=emailISEMPTY%5EORinclude_members%3Dtrue%5Eactive%3Dtrue&sysparm_view= If you have groups with 20+ members and no group email, it may be better to define a distribution list in your email system and to use that distribution list's email as the Group Email: /sys_user_grmember_list.do?sysparm_query=group.include_members%3Dtrue%5EORgroup.emailISEMPTY&sysparm_view= Check with your email administrators to see if it is possible to turn off recipient validation for the email account used by your instance, as this may take 100 ms to 10 seconds per recipient depending on email system being used. In such a scenario, it may take the instance 15 minutes to transfer a single email to the email server if the email has 100 recipients, blocking all other emails.Check if there are any scheduled reports with many recipients in the Users, Groups (especially groups with no group email), Email Addresses fields, scheduled to run during business hours /sysauto_report_list.do?sysparm_query=active%3Dtrue%5Erun_type%3Ddaily%5EORrun_type%3DperiodicallyRelated LinksEmails sent from custom SMTP email account ProofPoint are sometimes stuck in a send-retry loop Custom SMTP Server fails sending emails with error "Local address contains control or whitespace" Outbound emails are failing with invalid addresses blocked by Spamhaus with custom configured SMTP Server