SharePoint 2010 and SharePoint 2013 use the same IIS 6.0 SMTP server for incoming e-mail configuration. Because of the default configuration the incoming e-mail size limit is set to 2048 KB.
The error that your receive when you try to send an e-mail larger then 2MB or that has attachments larger then 2MB is something like this:
This message is larger than the current system limit or the recipient’s mailbox is full. Create a shorter message body or remove attachments and try sending it again.
You will have to go to IIS 6.0 administration console end right click the domain and then go to the Messages tab. In the message size limit you can enter the desired size for the incoming e-mail messages.
After you change the message size you will have to do an IIS reset to apply the changes.