Please try this instead:
ALTER TRIGGER [dbo].[SendEmail]
ON [ABCJun28].[dbo].[ABC_DB_OnlineFormsConfirm]
AFTER INSERT
AS
SET NOCOUNT ON
EXEC msdb.dbo.sp_send_dbmail
@profile_name = 'Gmail',
@recipients = 'ABCwebmaster@abc-inc.com;DEFwebmaster@def-inc.com', --';other_recipient@other_address.com;...'
@subject = 'An ABC Online App Has Been Completed',
@body = '',
@query = '
select
''Confirmation Code: '' + I.ConfirmationCode + NCHAR(13) + NCHAR(10)
+ ''Subject to Backup Withholding?: '' + ISNULL(F.IRSBackup, ''?'') + NCHAR(13) + NCHAR(10)
+ ''Form Type: '' + ISNULL(F.FormType, ''?'') + NCHAR(13) + NCHAR(10)
+ ''Website User ID: '' + ISNULL(F.userid, ''?'') + NCHAR(13)+NCHAR(10)
from Inserted I
LEFT JOIN ABC_DB_OnlineForms F
ON I.FormId = F.FormId
',
@attach_query_result_as_file = 0
GO