The maximum message size is 25MB.
However, whilst that's what will work at TalkTalk Mail there is no guarantee that the end to end message chain will send on such messages. I carried out a test, albeit a few years ago, checking the sending and receiving of messages within the UK. On the chosen test routes using mail services at either end both capable of handling 25MB total message size I found that the reliable sending and receiving required messages of 16MB or less. My recommendation is therefore to test before committing to sending large messages and in any event to limit attachments to no more than 12MB.
But why send large messages anyway when secure servers are available to upload messages to and those messages can be downloaded from there. My solicitor uses a specialist solicitor approved service to upload documents to and I can download them as required.
