I detected that the mailer is for some multi jobs not sending unstable mails.
Both multi jobs have the same configuration regarding mailer.
I attached both build.xml files, where I replaced all internal names with xxx,yyy,zzz,aaa, Same replacement means same text.
The multi job which does not send mail, is logging out:
An attempt to send an e-mail to empty list of recipients, ignored.
Jenkins version is 2.27
Mailer version is 1.18
Multijob plugin is 1.22
TFS plugin version 3.2.0, since it is last version which supports TFS2005
all other installed plugins are latest