At McAllister Litho Glasgow Ltd ("MLG") we take our data protection responsibilities seriously. Which is why we use MailBigFile's Business service to exchange large files with you. Your files will automatically be encrypted in transit and when at rest on MailBigFile's fully-patched servers in Ireland.
You can view MailBigFile's Security Policy here: https://www.mailbigfile.com/securitypolicy/
If the file(s) you are sending us contain "personal data" (any information relating to an identified or identifiable natural person) or "sensitive personal data" (data consisting of racial or ethnic origin, political opinions, religious or philosophical beliefs, trade union membership, genetic data, biometric data, data concerning health or data concerning a natural person's sex life or sexual orientation) then we strongly recommend that you encrypt the data prior to upload. This will ensure that no third-party (including MailBigFile) can gain access to the personal data.
7-Zip (https://www.7-zip.org/) is free open source software that can be used to create encrypted file archives.