I came across an issue while trying to send emails using email distributor batch job in AX 2012. If 10 entries are created in email sending status form, only one of them is emailed and rest of them were failing. I have found the reason for this in LCS and the reason is mentioned below:

SysEmailDistributor can only send one email with same attachment name in batch due to WinApiServer::FileDelete not removing files when called in common intermediate language (CIL).

Microsoft has confirmed that this is an issue, but they are not fixing at this time. More details can be found at the following link:

https://fix.lcs.dynamics.com/Issue/NotFixed/313591?bugId=1651803&qc=baf7c6ff636fd40738c7cc6618d53fce

So, the only resolution is to have different file name for your email attachments. For instance, if you are sending sales order invoice to your customer, you can have the sales order invoice number as your attachment file name.