Are The Senders Email Credentials Present And Up To Date?

In the Queue check the column labelled Sender to check who is sending this email. This staff user will need to login to their account and navigate to Settings > Update Incoming and Outgoing Email > Outgoing Email and ensure they have added their outgoing email details.

Has a To Email Address Been Added?

In the Queue click edit next to the email, check the To box on the right, if this is empty then no email address has been added and this is why the email isn't sending, just add an email address here and click the option to send the email

If no email address was added to the email this is likely to be because no email address is present on the client's file, or the email address stored on the client's file is incorrectly formatted so we would recommend checking this data. 

Has More Than One Email Address Been Added But They Are Not Comma Separated?

In the Queue click the Edit button next to the email, in the To field if you have more than one email address present they need to be separated with a comma only.

Has More Than One BCC Address Been Added?

In the Queue click the Edit button next to the email, in the BCC field if you have more than one email address present this email will not send, you can only include one address by BCC. 

Corrupted Attachment

In the Queue click the Edit button next to the email, if an attachment has been included is there an error message showing next to it to advise the the attachment is corrupt? If there is then you'll need to remove the current attachment and upload it again