If you have multiple PSMail accounts, you can pay for them all at once (and you may qualify for a discount!). To pay for all your accounts at once:
Step One: Visit https://mail.psmail.net/renew/
Step Two: When prompted, enter all your PSMail email addresses separated by commas (e.g. username@psmail.net, username2@psmail.net).
Step Three: Follow through with your payment using the Pay Now button.
If you renewed several accounts but the renewal did not apply to all of them, please contact billing (billing@psmail.net) with details of the transaction.