The reason for this is that consumer email accounts are supposed to be used by individuals to send messages to other individuals or small groups. They're not designed to be used to send bulk emails, which is what you're sending with Pianola.
The large email providers - such as those listed above - participate in a scheme called DMARC (https://dmarc.org) which identifies mass emails originating from consumer email addresses. When one provider that participates in DMARC receives an email that claims to be from another provider that also participates in DMARC it is likely that your email message will be rejected, bounced, or treated as spam.
The way to avoid problems is to use an email address that is linked to a domain that is owned by the club itself. If your club doesn't already have a web domain it's cheap and easy to register one. GoDaddy is usually a good place to check but there are lots of companies that will allow you to register a domain.
Once you have your own domain you can create an email address that you can use in Pianola in your club settings.
Finally, as an added verification measure, you can add something called an SPF record to your domain which confirms to recipients' spam filters that Pianola is authorised to send emails on behalf of your domain.
Here's what you need to add to your domain name settings:
v=spf1 a mx include:sendgrid.net ~all
If this all sounds like gobbledegook to you, don't worry - it's pretty technical stuff! But we can help.
Just contact firstname.lastname@example.org and we'll help you through the whole process.