re :''the employees emails are not showing up for 24 hours in the inbox of the AOL.com email recipient.'' After Thunderbird has sent emails via smtp server then it has no further impact on what occurs next. Email is now in the hands of various servers. You need to find out when it has been received into the recipients webmail account. Not sure what email client the recipient is using, if any at all, but obviously it cannot be downloaded if not there. Is the recipient in the same time zone? 'Are both senders and recipients computers showing correct time and timezone? Did they loggon to read emails in the same day? To test when the email is received: create email and select : 'Tools' > 'Delivery status notification' and also 'Return Receipt' Some servers will provide notification but others do not - worth trying anyway. Send email and then ask recipient to logon to their webmail AOL.com mail account using a browser and check for new mail. Usually there is a small difference in the 'Date' and 'Received' times as shown the column headers in thunderbird. Looking into the Source code of the email would offer more information. In Thunderbird thats, select email so it shows in Message Pane, clickon 'More' and select 'View source'. I did locate some info which sounds likely: http://kb.mailchimp.com/delivery/deliverability-research/my-subscribers-arent-receiving-my-campaigns ''emails are held up by AOL because they deliver in small batches which can sometimes result in emails taking up to 24 hours to be delivered to a specific email account.'' Using google, I have found a few reports about AOL emails being delayed in receiving. https://www.icomex.com/support/32-why-are-my-emails-delayed http://ask-leo.com/why_does_email_take_so_long_to_be_delivered_sometimes.html