Approximately 10k emails sent in one mass email campaign takes 1.5 hours time:

There are a lot of different aspects that can factor in the time it takes to deliver emails. There is the time it takes Salesforce and SendGrid to process your requests but there is also the time related to recipient servers accepting requests and filtering messages on their end.

Your Salesforce instance may have a lot of apex jobs that are taking up the shared resources time which may be one factor.

SendGrid Processing Times

The speed at which SendGrid processes your requests will depend on if you are sending via SMTP, /v3/mail/send, or Marketing Campaigns. For example, there are rate limits on how frequently you can call the v3 Mail Send endpoint. Currently, you may make up to 10,000 requests per second to our endpoint. Each email you send may include up to 1000 recipients.

Please let me know if this client uses SMTP or Marketing Campaigns.

We also allow you to safely test your sending speed.

We have configured a special domain for any users who are interested in testing out SendGrid's relay speeds at higher volumes without it negatively impacting your reputation. You can send your test messages to any address while still using our standard integration practices. All messages to this domain are accepted for delivery and then immediately deleted.

Recipient Time Considerations

Do you know what volume this client sends currently?

If this client has a good sending reputation and their dedicated IP address is warmed to send high volumes, recipient servers are generally willing to accept a large number of requests in a short period of time. If this client is new or sends lower volumes, they will likely want to warm up their IP to the target volume to avoid excessive delays on the recipients' end.

For example, if this client sends 50,000 messages daily and then their volume spikes to 1 million, it is likely they will experience delays as recipient servers throttle their email to better understand the spike. I have included a conservative daily warmup schedule here for you to reference.

Since there are a variety of different factors that impact delivery time between SendGrid and recipients, we do not have a table that displays the approximate time it takes to deliver emails by the volume. I do apologize for the inconvenience.

The processing times on SendGrid's end are dependent on the limitations of our system. The processing times for recipients is generally related to your domain/IP reputation and your previous sending volume.

Please reply at your earliest convenience. Also, feel free to let me know if you have any other questions or concerns.