1. Don't use strict (adkim=s; aspf=s) if you expect your emails to be forwarded (https://www.dmarcanalyzer.com/forwarding-within-dmarc/).
2. Microsoft (Outlook/Office365) ignores DMARC p=reject by default (https://docs.microsoft.com/en-us/microsoft-365/security/offi...)
Neither of this settings have anything to do with forwarding.
aspf and adkim are for SPF/DKIM alignment, where 'r' (relaxed) allows subdomains, and 's' (strict) does not.
aspf=s requires RFC5321.MailFrom and RFC5322.From to match exactly (no subdomain difference) for the SPF to be qualified as aligned.
adkim=s requires the DKIM key to be published under the same subdomain as found in the RFC5322.From address for the DKIM to be qualified as aligned.
Forwarding will break SPF in most cases anyway, this is unrelated to your aspf setting (unless you are forwarding between your own subdomains).
DKIM should not break by forwarding, regardless of your adkim setting, because forwarding does (should) not rewrite the RFC5322.From address.
For more explanation, see here: https://www.mailhardener.com/kb/dmarc#relaxed-vs-strict-mode
> 2. Microsoft (Outlook/Office365) ignores DMARC p=reject by default (https://docs.microsoft.com/en-us/microsoft-365/security/offi...)
They don't ignore it, they treat it similar to p=quarantine. So there still is a difference between p=none (or no DMARC at all) and p=reject.
https://en.wikipedia.org/wiki/Authenticated_Received_Chain
1. Don't use strict (adkim=s; aspf=s) if you expect your emails to be forwarded (https://www.dmarcanalyzer.com/forwarding-within-dmarc/).
2. Microsoft (Outlook/Office365) ignores DMARC p=reject by default (https://docs.microsoft.com/en-us/microsoft-365/security/offi...)