Error while trying to set up K-9 Mail client

I am trying to set up my RiseUp e-mail account with K-9 Mail client and I’m having an issue. I know RU has dropped support SSL certificates because of security reasons (“The secure connection may be of type TLS or STARTTLS. For security reasons, we no longer support SSL.”), and the error that I’m receiving is because of an unrecognized SSL certificate, should I worry or should I not?

This is the error:

The server presented an invalid SSL certificate. Sometimes, this is because of a server misconfiguration. Sometimes it is because someone is trying to attack you or your mail server, If you’re not sure what’s up, click Reject and contact the folks who manage your mail server.

(java.security.cert.CertPathValidatorException: Trust anchor for certification path not found.)acd25b5fdb Certificate chain[0[: Subject: CN=.riseup.net, OU=PositiveSSL Wildcard, OU=Domain Control Validated Subject has 2 alternative names Subject(alt):.riseup.net,… Issuer: CN=Sextigo RSA Domain Validation Secure Server CA, 0=Sectigo Limited, L=Salford, ST=Greater MAnchester, c=GB Fingerprint (SHA-1): af121b43c05056f1103461eb50d7ba45193a3f97 Certificate chain[1]: Subject: CN=Sectigo RSA Domain Validation Secure Server CA, 0=Sectigo Limited, L=Salford, ST=Greater MAnchester, C=GB Issuer: CN=USERTrust RSA cCertification Authority, 0=The USERTRUST Network, L=Jersey City, ST=New Jersey, Cb=US Fingerprint (SHA-1): eea3a14b

Reject Key/Accept Key

i mean error and solution in message, there is problem with their ssl certificate and they should fix it and its not problem from your side so all you can do is just contact them as message said also i’m not pro at SSL certificates but i guess if its broke that means it can easily decrypt connection OR it just like app confused and not sure if its right certificate for domain or not and in that case your connection still secure tho from hackers

I think that this is what’s happening, the application tries to find an SSL certificate since I guess it’s what you would expect from most e-mail providers, but since RiseUp has stopped support for said certificate, the application founds nothing and it gives me that message. This could simple mean that there’s nothing wrong with the security of my e-mail and that it’s just a normal procedure when K-9 does not find SSL.

as i said before it could have 2 meanings: 1. there is certificate but not made for riseup themselves like using other domain in it but it wont really hurt your security (i mean maybe it do but it will protect you from man in the middle attack) OR 2. that the certificate itself is broken and this will effect your security

No problems here. But I have been using K-9 with riseup for a few years.
If you haven’t already take a look at the guide,
https://riseup.net/en/email/clients/k9

I’m pretty sure that I did the same things while trying to set it up, but it throws me the same error, I’m going to try again, but I think that guide may be before they disabled SSL since they tell you to select that option.

Nope, same error, that guide is outdated.