Troubleshoot slow outbound email processing with custom SMTP serversIssue <!-- /*NS Branding Styles*/ --> .ns-kb-css-body-editor-container { p { font-size: 12pt; font-family: Lato; color: #000000; } span { font-size: 12pt; font-family: Lato; color: #000000; } h2 { font-size: 24pt; font-family: Lato; color: black; } h3 { font-size: 18pt; font-family: Lato; color: black; } h4 { font-size: 14pt; font-family: Lato; color: black; } a { font-size: 12pt; font-family: Lato; color: #00718F; } a:hover { font-size: 12pt; color: #024F69; } a:target { font-size: 12pt; color: #032D42; } a:visited { font-size: 12pt; color: #00718f; } ul { font-size: 12pt; font-family: Lato; } li { font-size: 12pt; font-family: Lato; } img { display: ; max-width: ; width: ; height: ; } } When using a custom SMTP server for outbound emails, admins may experience slow email performance, frequent SMTP Sender alerts, and a growing queue of sys_email records waiting to be sent. If you use your own mail server for sending emails as configured in the email account settings, you might encounter the following: Delays with high-volume notificationsReceipt of automated SMTP Sender alerts when jobs take longer than 30 minutes to completeErrors like "you've reached your 24 hour limit for message recipients." Release<!-- /*NS Branding Styles*/ --> .ns-kb-css-body-editor-container { p { font-size: 12pt; font-family: Lato; color: #000000; } span { font-size: 12pt; font-family: Lato; color: #000000; } h2 { font-size: 24pt; font-family: Lato; color: black; } h3 { font-size: 18pt; font-family: Lato; color: black; } h4 { font-size: 14pt; font-family: Lato; color: black; } a { font-size: 12pt; font-family: Lato; color: #00718F; } a:hover { font-size: 12pt; color: #024F69; } a:target { font-size: 12pt; color: #032D42; } a:visited { font-size: 12pt; color: #00718f; } ul { font-size: 12pt; font-family: Lato; } li { font-size: 12pt; font-family: Lato; } img { display: ; max-width: ; width: ; height: ; } } All supported releases Cause<!-- /*NS Branding Styles*/ --> .ns-kb-css-body-editor-container { p { font-size: 12pt; font-family: Lato; color: #000000; } span { font-size: 12pt; font-family: Lato; color: #000000; } h2 { font-size: 24pt; font-family: Lato; color: black; } h3 { font-size: 18pt; font-family: Lato; color: black; } h4 { font-size: 14pt; font-family: Lato; color: black; } a { font-size: 12pt; font-family: Lato; color: #00718F; } a:hover { font-size: 12pt; color: #024F69; } a:target { font-size: 12pt; color: #032D42; } a:visited { font-size: 12pt; color: #00718f; } ul { font-size: 12pt; font-family: Lato; } li { font-size: 12pt; font-family: Lato; } img { display: ; max-width: ; width: ; height: ; } } Custom SMTP servers have disadvantages compared to the default ServiceNow SMTP account provided with your instance. ServiceNow mail servers are physically closer to your instance host and ServiceNow SMTP servers are designed for rapid email delivery. Using external SMTP servers can experience latency and slower email processing because servers may need to run additional checks for domains, relay permissions, and other validations. Two main causes for email delays when using external SMTP servers: Your SMTP server may be unable to handle the volume of emails from your instance. For example, if your instance generates 100 emails per minute during peak hours, your email server must be able to accept 100 emails per minute.You may have groups configured with many individual recipients instead of a group email. Due to SMTP protocol requirements, recipients are added one by one during sending. For example, if your instance sends an email with 100 recipients, and it takes 100 ms to send each recipient command to your SMTP server, it will take 100 × 100 = 1,000 seconds (about 1.5 minutes) just to add all recipients. If your email server has latency or performance issues and takes 1 second per command, that single email will take over 15 minutes to process. Since emails are sent sequentially, all other emails in the queue are delayed as well. Resolution<!-- /*NS Branding Styles*/ --> .ns-kb-css-body-editor-container { p { font-size: 12pt; font-family: Lato; color: #000000; } span { font-size: 12pt; font-family: Lato; color: #000000; } h2 { font-size: 24pt; font-family: Lato; color: black; } h3 { font-size: 18pt; font-family: Lato; color: black; } h4 { font-size: 14pt; font-family: Lato; color: black; } a { font-size: 12pt; font-family: Lato; color: #00718F; } a:hover { font-size: 12pt; color: #024F69; } a:target { font-size: 12pt; color: #032D42; } a:visited { font-size: 12pt; color: #00718f; } ul { font-size: 12pt; font-family: Lato; } li { font-size: 12pt; font-family: Lato; } img { display: ; max-width: ; width: ; height: ; } } For email server capacity issues: Discuss email processing capacity with your email server administrator.Gather diagnostic information: Select the Enable debug output option in the sys_email_account record.This outputs all communication between your instance and mail server to the node logs.Download the node logs by following the article How to download localhost logs from all or selected nodes.Look for lines containing DEBUG: SMTP or DEBUG: IMAP, for example: 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 These logs include all SMTP commands sent with millisecond timestamps. Share these logs with your email administrator to help identify response time issues. Important: Turn off debugging after troubleshooting, especially in production instances. Debug mode logs all email traffic including content, which can: Fill node logs quickly (several gigabytes)Cause log truncationMake logs unusable for troubleshooting other issues For recipient configuration issues: This problem is most noticeable with first-level assignment groups that receive many notifications when records are assigned to them. 1. Check if your groups have a group email set and that Include Members is not selected unless necessary. Go to: /sys_user_group_list.do?sysparm_query=emailISEMPTY%5EORinclude_members%3Dtrue%5Eactive%3Dtrue&sysparm_view= 2. For groups with more than 20 members and no group email: Create a distribution list in your email systemUse that distribution list's email as the Group EmailCheck affected groups at: /sys_user_grmember_list.do?sysparm_query=group.include_members%3Dtrue%5EORgroup.emailISEMPTY&sysparm_view= 3. Ask your email administrators if they can turn off recipient validation for the email account used by your instance: Validation can take 100 ms to 10 seconds per recipient depending on the email systemWith 100 recipients, a single email could take 15 minutes to process, blocking all other emails 4. Check for scheduled reports with many recipients that run during business hours: Look for reports with many users, groups (especially those without group emails), or email addressesGo to: /sysauto_report_list.do?sysparm_query=active%3Dtrue%5Erun_type%3Ddaily%5EORrun_type%3Dperiodically Related Links<!-- /*NS Branding Styles*/ --> .ns-kb-css-body-editor-container { p { font-size: 12pt; font-family: Lato; color: #000000; } span { font-size: 12pt; font-family: Lato; color: #000000; } h2 { font-size: 24pt; font-family: Lato; color: black; } h3 { font-size: 18pt; font-family: Lato; color: black; } h4 { font-size: 14pt; font-family: Lato; color: black; } a { font-size: 12pt; font-family: Lato; color: #00718F; } a:hover { font-size: 12pt; color: #024F69; } a:target { font-size: 12pt; color: #032D42; } a:visited { font-size: 12pt; color: #00718f; } ul { font-size: 12pt; font-family: Lato; } li { font-size: 12pt; font-family: Lato; } img { display: ; max-width: ; width: ; height: ; } } Emails 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" How to resolve outbound email failures due to Spamhaus blocks