I use email but specifically POP3 email, not IMAP email.
I will not use Gmail or some other online service. I use POP3 accounts and a local email client. This allows me to download emails and file them locally as well as back up everything. I simply can not bring myself to rely on some other server out there to be as dedicated and complete with backups and retention of information. (all this in addition to the Gmail data mining).
I know IMAP (Gmail, Hotmail, etc) is the form everyone thinks is best. But it's not always. While IMAP is great for accessing the same email from several clients, IMAP is not the best in terms of utilizing email for work procedures for me. POP3 allows me to access mail from any client, I merely have to set up the client properly. In addition POP3 allows me to delete things locally and leave a copy on the server for a given time if needed. I can delete a POP3 email and then go retrieve that deleted message from the server days later if the deletion was a mistake.
In my local email client I have folders for each client then some general folders for other email items:
- personal items
- client 1
- Project A
- Project B
- Project C
- client 2
- client 3
- Outstanding Invoices
- Paid Invoices
I keep all "to do" items in the inbox - read or unread. If it's in my inbox it needs attention. When an email is read and the tasks are completed, I file the email in the correct folder. So, I don't have any issue with things being red or unread. If something is unread.. it just means it's unread and I don't know what it entails. If I've replied to an email, there's a little arrow next to it indicating I've replied. All attachements are downloaded so I have those, and they are backed up as well.
I use filters for outgoing mail to automatically file things as needed. A filter for @client1.com will file all outgoing mail into Client 1's folder. A subject line with the word "Invoice:" in it files the outgoing email into "Outstanding Invoices". And so on.
My "mail" folder is backed up nightly and if there should ever be an issue I can simply set the client to "re-download messages from server" which will go grab everything still sitting on the mail server. I leave all messages on the server for 14 days, even if they are deleted locally.
I've tried to use services like Trello but I found I spent way too much time transferring data from emails to the service needlessly. All the information I need is in the emails. It's a waste of time for me to use any other service.
In the end, I've found nothing as workable as a POP3 email client has been.. and I've been using email this way going on 20 years.