Sending Attachments Via Express Email Sending Large Attachments through Express webmail Within the SMTP security window under the "Anti-Denial of service" please ensure that you are not restricting the "throughput from each host". You can add friendly IP/Domains within the Friendly hosts lists to except certain IP addresses from this limit. You will find that the attach popup window in MailSite Express will take longer to upload and close, larger the files you are attaching to the email. Rockliffe suggest that FTP is used for files greater than 2 MB, this will help keep your server running efficiently.