Getting delayed Email notifications?

Possible Reasons for Mail Delay:

While sending an email:

Slow connection/delayed response time.
Internet slowness/Network latency while trying to connect to the mail server.
Mail server availability and its response time.
Firewall processing time at the network.

While receiving e-mails:

Anti virus scanning in mail box.
Processing of spam filters in mail box.
Increased load of incoming mails.

Note: Mail server connection time should be less than 100ms (especially when there is a larger number mail to be sent each minute).

Troubleshooting steps:

Check with your network administrators on network latency, firewall processing, mail server response time.
Reduce the overall mail server connection time to 100ms or less if possible.
Configure Notification Profile for devices and alarms only if required.
Select only required trap processors/Event log monitors/Syslog rules in Notification Profile criteria. Avoid using "select all" unless it is necessary. Mostly traps/syslog/event logs are expected to receive in bulk raising more alarms per minute.
Avoid using wildcards while creating SNMP Trap Processors.
Monitor the trap flow for an hour/day and then create trap processors, configure Notification Profile criteria with respect to the flow. This will avoid processing all incoming traps thus keeping the alarm load in control.
Ensure the script response of Run Program Profile/Run System Command is lesser, if any such profile is configured. If the script response time is higher then the upcoming mails will also be delayed as all Notification Profiles work in single queue.

For assistance, you can reach out to us here.

Importance of Mail server connection time:

Email/Email-SMS Profiles are configured to send emails of the alarms in case failures are detected.
To send mails immediately after the alarm is raised, the mail server connection time is crucial.
Sending an e-mail from Notification profile includes testing mail server connections, connecting to the mail server and sending an e-mail.
Lesser the mail server connection time, the lesser delay in the mail received.

Alarm load and Email delay:

The time taken to send an email relies on the number of alarms per minute.
This is because Notification profile works in queue, it will be processed one after another. If there are more alarms (configured to send an email) per minute, and the mail server connection time is higher, the delay in receiving mails will increase with time due to accumulation.

Every second in mail server connection time matters when more alarms are raised per minute. The same is explained below with the example of 10 alarms raised per minute:

Alarm Pattern	Alarm load (Alarms raised/minute)	Is Notification configured for all alarms?	Time taken to test mail server connection (approx.)	Time taken to send email (approx.)	Email delay for the first alarm of the minute (approx.)	Email delay for the last alarm of the minute (approx.)	Mail delay after an hour (approx.)	Is critical?
10/min-[every minute]	10	Yes	5s	5s	10s	1min 40s	1hr 40min	Yes
10/min-[every minute]	10	Yes	500s	500s	1s	10s	1min	No
10/min - [10 alarms at a time once in an hour]	10	Yes	5s	5s	10s	1min 40s	1min 40s	No
10/min - [10 alarms at a time once in an hour]	10	Yes	500ms	500ms	1s	10s	10s	No
10/min [every 5mins 1 alarm, sometimes every 10mins 1 alarm]	10	Yes	5s	5s	10s	10s	10s	No
10/min [every 5mins 1 alarm, sometimes every 10mins 1 alarm]	10	Yes	500ms	500ms	1s	1s	1s	No