I can't send email after 6PM

Based on the error message you're receiving, it appears you're encountering a sending limit issue with AWS WorkMail. This error message typically appears when you've reached the maximum number of messages you can send within a specific time period.

AWS WorkMail has sending limits that reset on a rolling basis (usually within a 24-hour period), which explains why you're able to send emails again in the morning. The error "You are currently not allowed to send this e-mail. Please try again later" is commonly associated with hitting these sending quotas.

Since the issue is affecting both your account and your cofounder's account at different times, it suggests you might be approaching the sending limits for your organization.

To resolve this issue, you could:

1. Check your sending activity to ensure you're not exceeding any daily or hourly limits. WorkMail has a daily sending limit of 10,000 recipients per user in a rolling 24-hour period, but there might be additional restrictions on your specific account.

2. If you need to send a large volume of emails, consider using Amazon SES directly for mass or automated mailings, while keeping WorkMail for normal business communications.

3. If you believe this is happening despite low email volume, you may need to contact AWS Support as there could be account-specific restrictions or technical issues affecting your ability to send emails.

4. Verify that your WorkMail has the proper permissions to use SES for sending emails by checking the authorization policies in your SES console under Verified Identities.
   Sources
   Amazon WorkMail You have exceeded the sending limit for this account. | AWS re:Post
   Undelivered Mail Returned to Sender | AWS re:Post
   Sending Email failed in Workmail | AWS re:Post