It really depends on the type of email you send. It’s best to send verification emails right after a user takes an action, so they can continue the process that requires verification. For example, when a user creates an account using their email address, they should receive a verification email right away, be able to confirm their email, and take the next steps.
The same applies to welcome emails and confirmation emails, which should be sent immediately after a user creates a customer portal account and successfully verifies it so that they can continue the signup process and access the portal as soon as possible.
A reset password email is no different. You must send a password reset email immediately after a customer portal user makes the request, or, asks you for help with setting up a new password. If a user has to wait more than a few seconds for a password reset email, they may give up and be left without access to the customer portal.
When it comes to a feedback email, it really depends on how customers use your customer portal. However, don’t wait for too long before asking them for their opinion. Sending this email up to 10 days after a customer started using the customer portal is a good idea.
The rule is pretty much the same when you want to send an invitation email. Ideally, you should send the email a few days (or weeks, depending on the complexity of your product/service) after a customer starts using your product/service. Lead them through the onboarding process first, let them get to know your product and absorb all of the available data, and then inform them about the possibility of joining the customer portal.