MATLAB started using Java 7 from R2013b. Java 7 uses IPv6 by default.
Could you please try the below workaround:
1) At the command line, enter:
>> which -all java.opts
If it says "'java.opts' not found.", then proceed to step 2.
2) Go to your MATLAB startup directory. Create a file "java.opts" with the below one line:
3) Restart MATLAB, and try the "sendmail" function again.
If a "java.opts" file was already found in step 1, open that file. Copy and paste this line into that file:
Save the file, then restart MATLAB.
This will tell MATLAB's version of Java to use IPv4 for communication when possible.
Hope this helps!