I'm looking for a Microsoft Outlook and E-mail expert for setup advice on E-mails

Hello, I am looking for some advice and help setting up e-mails within Microsoft Outlook using several domains. I have a main domain, for example www.maindomain.com which is a holding company for several other websites recieves all e-mails from all the other websites, and they all come in centrally. This I understand and I can put forwarding on the other domains and forward all mail onto the the main domain or e-mail. BUT I want to be able to reply from all the seperate e-mail accounts. So when you click "New mail", I can type my response and choose the e-mail I send it from and also the signature. By having several e-mail addresses all setup seperatley it's a maintenance nightmare expanding each e-mail to see sub folders. The budget is £25 but this can increase depenat on the work and feedback you give me. Please let me know what is achievable. Thanks Liam