Why not try using wetransfer.com to send your pre-masters? Both participants will receive email notifications for the transfer and it is free for transfers up to 2GB.
Price per master:
Vinyl master @ £45(GBP)
Digital master @ £35(GBP)
Please specify 'dynamic' or 'loud' when ordering digital mastering.
10% discount for large projects with 5 or more tracks.
Get in touch for more information on stem mastering and mix project pricing.
Guidelines for preparing pre-masters:
Please ensure you turn off any compressors or limiters on your output channel when you bounce your files.
The pre-master files must be in either .wav or .aiff format and at a minimum resolution of 24bit @ 44.1kHz.
The volume of the pre-master should be around -5dB to -3dB at it's maximum peak so there is headroom to process the audio for you.
You can check your file by loading it into an audio editor and comparing it with the two examples below :
Here is a pre-master file at the correct level of around -4dB. As you can see there is headroom between the loudest peak and 0dB (the maximum volume).
Here is the same pre-master file where the main output's limiter has been left on! As you can see there is no headroom whatsoever between the loudest peak and 0dB!
If your file looks like the example directly above, your DAW may be clipping because the main output volume is too high or you need to check for compressors or limiters that have been mistakenly left on the main output while bouncing your file.