Email Attachment Size
15MB is the maximum size of an unencrypted email that includes a brief amount of text and a digital signature.
12MB is the maximum size of an encrypted mail that includes a brief amount of text and a digital signature.
The reason this varies is because encryption will add to the total size of an email and the size limitation on the emails themselves are for the total email which includes the text and any potential signature, encryption, or attachment.
If you require the ability to transmit a file size larger than AKO/DKO mail will allow you to send please use our Files Section.
Per NETCOM guidance 2004-11A certain file types are not permitted to be sent through the AKO/DKO mail system. These attachments are blocked in an effort to combat the spread of viruses; the list of blocked attachment types is as follows:
.ace, .ad, .ade, .adp, .asp, .b64, .bas, .bat (& .bat.), .bhx, .ce0, .ceo, .chm, .cmd, .com (& .com.), .cpl, .crt, .dbx, .dll, .doc.bat, .doc.com, .doc.pif, .dot, .eml, .exe (& .exe.), .hlp, .hqx, .hta, .inf, .ins, .js, .jse, .lnk, .mdb, .mde, .mim, .msi, .msp, .nch, .ocx, .pi, .pif, .rar, .reg, .scr, .sct, .shb, .shs, .txt.scr, .upx, .url, .uu, .uue, .vbe, .vbs, .vss, .vst, .vsw, .wmi, .wss, .wsc, .wsf, .wsh, .xxe, .zip
The majority of these file types are files that can be opened and executed on their own and thus can be programmed with anything including a virus. The rest of the file types are files that can contain these programs inside of them without immediately appearing to house any program at all. The risk for allowing these file types through is that a user could become infected and email all of their contacts with the same attachment who might then download and run the program again. Removing these attachments ensures that a user can have a reasonable belief that attachments are being sent by hand and not through a malicious script.
Your email must be digitally signed in order to successfully send an HTML file as an attachment. Per JTF-GNO and Army directives AKO/DKO must strip any HTML attachment from an email that is unsigned and replace it with a message that reads “This message contained an html attachment that has been removed by AKO/DKO in response to JTF-GNO and Army directives.”
AKO’s email policy can be found in the following document: https://www.us.army.mil/suite/doc/1828294
NETCOM TECHCON #2004-11 can be viewed here: https://www.us.army.mil/suite/doc/4558869
Note that you may be required to log in to AKO to view these documents.