Choosing an email address/provider for academic work as you change positons I'm an on-again-off-again academic, I guess you could say: I've switched positions in and out of academia several times over the past decade. When I write academic papers (or even Free Software in the context of academic work), I often face a dilemma regarding which email address to put down in my contact information. The dilemma is not always the same; I want to focus my question on two scenarios:


Research work you pursue "on your own time" which is not a (direct) part of what you work on at your current employer; and when you know your employment is likely to end soon.
Research work you pursue between periods of employment, or which your current employer is not interested in being associating with.


So, here are some options of what to use as your email in these scenarios, by no particular order:


An email account on the university you got your PhD from, which is guaranteed not to expire (as much as these things can be guaranteed), and does not indicate whether you are a student, or currently a faculty member etc. Example: your_name@alma_mater_uni.ac.xy
Your general-purpose personal email address at some large, free mail account provider. Example: your_name@gmx.com
A professional-affairs-only custom email address at one of the large, free email account providers. Example: your_name_academic@gmx.com, or your_name_phd@gmx.com or something better-sounding.
A personal email address at a smaller, academia-oriented mail account provider. (I don't know any of these but perhaps they exist - with free or paid accounts.) Example: your_name@academia-mail.com or your_name@academia-mail.edu
A professional-affairs-only email address at a smaller, for-pay mail account provider. Example: your_name@fastmail.com


Which do you believe is the best choice, and why?

A related question: Which email address should a student use in a publication?
After some of my personal e-mail hopping (also as corresponding emails on papers), I'd recommend getting a domain name and linking it to one of your email accounts. That is, only if you do not get to retain your academic email indefinitely if you have one (the uni I used to be at has the regulation to delete the e-mail and do no forwarding...)

By having your own domain, you can move services but keep the actual email consistent over time. I.e., you can use name@domain.org and where that points to just changes.

Any kind of service (and domain) that you cannot move around nor have any assurances for longevity on, are to be avoided IMO. I made that mistake with both my university and a corporate account so I learned the hard way...